[gtk] (8 commits) Non-fast-forward update to branch wip/otte/dnd

[Benjamin Otte <otte src gnome org>]

The branch 'wip/otte/dnd' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  b927755... contentprovider: Add a union content provider
  a5a86f3... dragdest: Handle NULL content formats everywhere
  73b609f... notebook: Move dnd scrolling via arrows to own drop target
  488449d... notebook: Use proper DND
  cdce402... placessidebar: Modernize DND

Commits added to the branch:

  9a7607b... contentprovider: Add a union content provider
  e25bfa6... dragdest: Handle NULL content formats everywhere
  9703fcc... notebook: Move dnd scrolling via arrows to own drop target
  27d7aa1... notebook: Use proper DND
  1145da3... placessidebar: Modernize DND
  c457e08... dnd: Port the TreeModel machinery to GValue DND
  fc51c47... tests: Modernize testdnd2
  09dffa6... Remove gdk_content_provider_new_with_formats()