Introducing TranslationStash

It's the place where sandboxed users can store their translations
before they are approved.

Also introduced whitelisting of write api modules. The list now
contains 'options' and 'translationstash'

Some minor unrelated changed due to sorting few lists and other
small cleanups.

Change-Id: I7c6b9747aa28fbc0e914e692f395f7afc64f4137
Merge "Introducing TranslationStash"