Test all the things!

This merge request improves the code coverage of the project's unit tests.

I broke up this rather large set of changes into separate commits. See the individual commit messages for details.

• 75773b6d - Use PHPUnit provided by Composer instead of downloading a PHAR
• 737771f2 - Convert dashes to underscores when converting to HTTP headers
• 08aaa966 - Group conditional logic for clarity
• 1477621c - Create missing tests for PreauthUserDetailsProvider, introduce an EnvironmentHelper
• b74fd618 - Federated preauth tests made consistent with new preauth tests, improved coverage, moved test data from JSON to source code
• 09d36d36 - LocalUserDetailsProvider throws Exception if JSON is invalid, returns null if JSON is missing
• d021fd72 - Verify missing attributes are set as false
• e29430a9 - Docblock and PSR-2 formatting improvements

PHP Trait

In 1477621c, I introduced a lesser-known feature of PHP called a trait. It allows one to "inject" common methods into any class without requiring inheritance.

@andrew-summers @weizhong-wang @KJOYNER

src/main/edu/wisc/doit/uwphps/preauth/FederatedPreauthUserDetailsProvider.php

@@ -34,15 +34,15 @@ class FederatedPreauthUserDetailsProvider extends UserDetailsProvider
 
         if ($this->httpHeaders) {
             $userDetails = new UWUserDetails(
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::EPPN)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::SPVI)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::FULL_NAME)),
-                explode(static::DELIMITER, getenv(UserDetailsProvider::httpHeaderFromAttribute(static::UDDS))),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::EMAIL)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::SOURCE)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::ISIS_EMPLID)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::FIRST_NAME)),
-                getenv(UserDetailsProvider::httpHeaderFromAttribute(static::LAST_NAME))
+                getenv($this->httpHeaderFromAttribute(static::EPPN)),
+                getenv($this->httpHeaderFromAttribute(static::SPVI)),
+                getenv($this->httpHeaderFromAttribute(static::FULL_NAME)),
+                explode(static::DELIMITER, getenv($this->httpHeaderFromAttribute(static::UDDS))),
+                getenv($this->httpHeaderFromAttribute(static::EMAIL)),
+                getenv($this->httpHeaderFromAttribute(static::SOURCE)),
+                getenv($this->httpHeaderFromAttribute(static::ISIS_EMPLID)),
+                getenv($this->httpHeaderFromAttribute(static::FIRST_NAME)),
+                getenv($this->httpHeaderFromAttribute(static::LAST_NAME))
             );
         } else {
             $userDetails = new UWUserDetails(