Overhaul watchlist UI [beta]

* Make watchlist main tabs adhere to design (fix colors, add border,
  make corners of 1st and last button rounded, change text to "All" and
  "Modified")
* Make watchlist items look similar to the provided design (fix padding
  and margins, make all the item, not only text, clickable)
* Make second level watchlist tabs adhere to design (and make the
  whole tab clickable)
* Remove date rows from watchlist (design uses "x days ago" instead)
* Make the recent changes view look like in design assets (adjust
  margins, padding, colors, add user icon)
* Fix thumbnails styles
* Small fixes in diff view (colors, make the end of the diff visible
  when scrolled to bottom)

Change-Id: I78ef0a9c75dd74ab8badbaea140a3cdd9137175c
Merge "Overhaul watchlist UI [beta]"