[gtk] (19 commits) Non-fast-forward update to branch wip/baedert/for-master

[Timm Bäder <baedert src gnome org>]

The branch 'wip/baedert/for-master' 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:

  ef30e0a... widget: Create style context in _init
  d84ab09... {box,grid}layout: Access border spacing directly
  1bf3e43... Adwaita: Fix levelbar styling
  394839b... calendar: Fix an uninitialized value
  cc367d8... calendar: Remove details
  adb7ea4... testcalendar: Remove unused function
  1b90dd6... calendar: Add accessors for display properties
  b2c0b93... calendar: Remove spinning code
  0330d84... calendar: Try to avoid changing size when changing the year
  f37e3c1... calendar: Use widgets for everything
  abc031e... calendar: Use GDateTime to select days
  8e08d85... calendar: Return a GDateTime from get_date()
  2c25a07... calendar: Keep a GDateTime around
  9b755dc... calendar: Remove month-changed signal
  e25c8ef... calendar: Remove an unused enum
  a9638ab... box: Move vfunc implementations before class_init
  033d48f... widget: Remove GtkWindow special case in create_render_node
  ea892a5... treepopover: Fix header guard
  0ca2fc3... window: Remove public user_ref_count API
  895866c... window: Make decoration a widget
  5ab8a0b... Rename gtk_widget{get,set,has}_style_class to _css_class

Commits added to the branch:

  596e7d7... {box,grid}layout: Access border spacing directly
  11de423... Adwaita: Fix levelbar styling
  31d6cb8... calendar: Fix an uninitialized value
  1328d9b... calendar: Remove details
  b3da971... testcalendar: Remove unused function
  cdd074d... calendar: Add accessors for display properties
  997a5fb... calendar: Remove spinning code
  6bf442c... calendar: Try to avoid changing size when changing the year
  61d6f29... calendar: Use widgets for everything
  83b6e41... calendar: Use GDateTime to select days
  8d5d9fa... calendar: Return a GDateTime from get_date()
  31a55e1... calendar: Keep a GDateTime around
  fa1937a... calendar: Remove month-changed signal
  507c01d... calendar: Remove an unused enum
  7c0fa11... calendar: Remove day-selected-double-click signal
  114ec80... box: Move vfunc implementations before class_init
  2a88b2a... treepopover: Fix header guard
  4355c76... Rename gtk_widget{get,set,has}_style_class to _css_class
  9eddaa2... window: Move variable initialziation just before usage