Add Special:Thanks as a non-JS fallback

If the user has JavaScript disabled, clicking
on "thank" will send the user to Special:Thanks
with the revision id already filled in. When
submitted, the form calls the API internally
and then shows the user an error or confirmation
message.

Special:Thanks is not a listed special page
since it's mainly intended as a fallback.

The API was modified to return the user name of the
editor who is being thanked if a new notification
was created.

Bug: 49161
Change-Id: I7ba4664b92bb0da425784350487ed0e7ca352b4e
Merge "Add Special:Thanks as a non-JS fallback"