Moves the jQuery.NativeEventHandler from WikibaseLib into ValueView extension

Introduces a few minor changes while moving this:
- Gets rid of all Wikibase/MediaWiki dependencies in tests.
- Some cleanup done in test files, moved basic test definition in separate file.
- Some coding style changes, most notably multi-var statements replacing single-var.
- Cleanup in comments and documentation.

Change-Id: I620e901594b31b40701079ac6be44e1f6fb1bec2
Merge "Moves the jQuery.NativeEventHandler from WikibaseLib into ValueView extension"