Updated documentation with @ingroup themeable so that theme functions can be picked up by the api module. Also did some minor documentation on theme functions without comments. Also got rid of old TODOs in comments which were no longer relevant. No code changes what-so-ever. by myself

Issue #146401

Issue #199590 by myself

Issue #199967 by Senpai

No code changes.

Issue #165065 by ocyrus

Issue #186154 by myself

Issue #199697 by myself

Issue #84863 by awong

No code changes.

Issue #198848 by ocyrus

Issue # 193840 by awong

Issue #198943 by ocyrus, BenjaminW and myself.

No code changes.

Issue #193840 by awong

This fixes tab issues making the code hard to understand.
Also fixes improper spacing caused by new patches to multichoice.module

Issue #198840 by ocyrus

Issue #198252 by ocyrus

Issue #198911 by myself

Issue #160205 by awong

No code touched.

Issue #155162 by ocyrus and Senpai

Issue #146403 by ksceirer

Issue #198241 by awong

Added a document header.