Add a multi account KindSectionView (E4)

* This allows us to treat all kinds (i.e. mime types) the
  same (except for name and photo).
* We can also set the icons and add empty editors naturally
  (w/o checking if the kind section is the last on in the list)
* Finally, we can also expand to the full editor in place now

Bug 23589603

Change-Id: Ibdecd8a9ef33cd1db70ffd9fd17e7883555d1fa4