Refactoring mw.Feedback to work with OOUI elements

Refactoring mw.Feedback to work with OOUI elements

Transform mw.Feedback into an ooui dialog.
* Added a configurable checkbox for useragent and terms
  of servvice options. The checkbox can be configured
  to be visible or not, and to be mandatory or optional.
  (useragent addition based largely on the unmerged
  fix I37b1a271af115)
* Transformed the 'feedback-bugornote' message to a
  configurable intro message with a link to the feedback
  page.
* Added a 'thank you' or 'error' dialog at the end of the
  operation indicating whether the feedback was sent or
  if there was some error.

Bug: T89878
Bug: T43291
Bug: T35365
Bug: T54588
Bug: T65290
Change-Id: Id1967a83a502f689c40f1af71398c3be99e30640