I'm replacing using the QThreadPool for handling all of the MDSplus
calls with a concurrent.futures.ThreadPoolExecutor.

There is a new function in mdsplushelpers called retrieve_all_data that
uses the ThreadPoolExecutor.  A keyword is a progress_signal. This is a
Qt signal that can be connected back to a progress bar to keep
functionality from before.  I should probably wrap the emitting in a
try except clause.

retrieve_all_data is called from an instance of a Worker using the
original QThreadPool in app.py. The done signal is connected to
handle_mdsplus_data.

I've removed handle_returning_data because it is no longer needed.  The
progress bar is updated via the new function update_progress_bar which
is connected to the worker progress signal.

I modified workers.py to pass its progress signal to retrieve_all_data.

ToDo:
    Decide on an timeout implementation detail.  I'm thinking about
    adding it to a global configuration.  It is nice to have, but it can
    take a long time to grab all of the data for long cathode plasmas.

I've decided to just leverage numpy for my type checking. I really only
want to deal with numpy arrays, so I removed the isistance check against
Iterable.

The truthyness now is simplier and just checks if len(self) is greater
than 1.  An implementation detail that I'm not sure if I like is it will
throw a ValueError if the lengths of time and data don't match.

Users can now empty the cache when they need to regrab data such as
after a change has been made on the MDSplus tree side.

The size of the cache can now be monitored via logging.

Added a function called empty_lru_cache function to empty the cache for
the decorated _retrieve_signal function.  I want the user to be able to
regrab data for the same shot if a modification has been changed on the
tree side.

Because data.Data is now truthy, I changed the check_data_dictionary to
leverage that functionality instead of checking against None.

Also, removed some old print statements.

I wanted to check the __init__ arguments to see if they are iterable. I
decorated iterable_validator with @staticmethod because it does not need
to know anything about the class name or instance.

iterable_validator will raise a ValueError if the data is not iterable.

Data class now can be 'truthy', has a defined length, and supports ==

ToDo: Redo the __repr__ function and __str__ functions.

I was encountering an error (see Issue #12 messages) where matplotlib
doesn't calculate the new subplot coordinates correctly.  There ends up
being a negative width or height followed by crashing the program.  I
don't seem to have this issue anymore by using gridspec.  However, I
needed to add some functionality to app.py to use
GridSpec.tight_layout() because Figure.tight_layout() wasn't working
like I thought would.

Created a helper function called _retrieve_signal where all inputs are
hashable so that @functools.lru_cache could be utilized.

retrieve_signal now unpacks some of the inputs and calls
_retrieve_signal.

Some of the logging messages were modified as well.

Continuing to add the @log decorator in places.  Made some modifcations
to some of the pyqt slot functions that needed an extra paramter that
isn't used.  I really don't understand why they didn't throw errors
before.  Probably something to do with how PyQt handles them.

Added some more logging statements to exception handling in
mdsplus_helpers.py

Double clicking update button would lead to a crash.  Button is now
disabled while grabbing data.  It is unclear if I just added a bug to
master.  Sorry!

A logging packaged was created with single module called
piscope_logging.

piscope_logging has three functions:
	create_logger: creates a logging.Logger instance
	log: decorator that logs calls and exceptions
	time_log: decorator that logs calls, exceptions, and time of
	execution

The decorators have been added in mdsplus_helpers.py, app.py.  The
logger creation has been modified in main.py

Notes: I've noticed that on some of my pyqt slots, I haven't included enough
arguments for the incoming pyqt signals.  This makes things crash if you
decorate the slot function.  I'm working on fixing this as we speak.

THIS IS UNTESTED. USE AT YOUR OWN RISK.

The way I check to see if xlim and ylim should be enabled is to see if
the key is in the config dictionary.  I wasn't deleting the key and
value from the dictionary when it should be.

Note on removing keys from dictionary:

dictionary_variable.pop(key_to_remove, None) will remove key_to_remove
and return the value of dictionary_variable[key_to_remove].  If
key_to_remove is not in dictionary_variable, then it will return None.

I changed the deleting code for signals to this intead of using python's
del function.

Needed to fix a similar issue when opening a config file at the start
with a bad server address

App would lock if there was a bad server address after opening a new
configuration file.  Now, it should move on gracefully and inform the
user that it couldn't access the server.

All of these files were before I started working on a true jScope
replacement.  They are no longer used and are now being removed from the
repository.

I was bad and didn't push earlier so now I have to deal with this merge.

Moved the axes modifications above the list of signals.

Added more docstrings to app.py

Fixed bug calling self.get_node_locs instead of parser.get_node_locs

Also created oes_config.ini with Halpha and Hbeta