Core: Use aria-describedby for non-label elements

Fixes #900
Closes #1083
ALL: Add plugin UMD wrapper, Closes #977
Core: Added radio/checkbox to delegate click-event

Reverts the accidental change from d319a0da35e5bdd0adad7f2233ce5fdd15969c74,
where these event handlers were dropped.

Closes #1126
Test refactoring
Tests: Further file splitting