Break long lines

Also:
* Remove an unneeded constant MEDIAWIKI check in a file with all classes.
* Document some variables.

Reduces PHP CodeSniffer errors and warnings.

Change-Id: I67bccf82e90302d13ad8fd04c8a4b75ac5edd984
Use capital for classes Languages and ExtensionLanguages

Searched core and 600+ extensions for uses. Found no more.

Class names are case-insensitive anyway.

Change-Id: I296d39be9aa3a2690f80a23691b34394aa1c6637
Merge changes I296d39be,I67bccf82

* changes:
  Use capital for classes Languages and ExtensionLanguages
  Break long lines