[gtk] (11 commits) Non-fast-forward update to branch stackpage

[Matthias Clasen <matthiasc src gnome org>]

The branch 'stackpage' 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:

  2a1ce8c... container: Add a function to get child metas
  f2db092... stack: Convert child properties to a child meta object
  9358931... Add docs for GtkStackPage
  36e6aeb... stack: Convert child properties to a child meta object
  b0cd8a3... Add a GtkStackPage::widget property
  22c73b8... builder: Allow specifying objects inline

Commits added to the branch:

  3ce664b... stack: Convert child properties to a child meta object
  8790e9a... builder: Allow specifying objects inline
  ad6ab9d... tools: Split gtk-builder-tool
  40fc5cf... builder tool: Rewrite the simplify command
  86ae4c4... Document --3to4
  72d0936... builder tool: Operate on multiple files
  dec97e2... Update ui files to new stack syntax
  771a7d4... Some small additions to the migration guide
  c96835f... migration guide: Mention --3to4
  6a0a7da... assistant: Convert child properties to a child meta object
  9f088c1... builder-tool: Convert assistant pages too