Merge branch 'restproxyattributebindingfilter' into 'master'

Add PviAttributeBindingFilter

AttributeBindingFilter is a filter that is used along with
rest-proxy to add headers to a request based on the attributes added
with the filter.

WIP for suggestions/critiques on the design and implementation.

Please review: @paul.erickson @ahoffmann @bjsousa 

See merge request !9