[gtk] (7 commits) ...Merge branch 'constraint-list-model' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  274c47e... constraint layout: Provide list models (*)
  a442e6e... constraint editor: Use the list models (*)
  377f0c1... constraint editor: Use name properties (*)
  c5e1b00... constraint editor: Implement saving (*)
  5a3cf5a... constraints editor: Stop naming constraints (*)
  aa86873... constraint editor: Implement loading (*)
  b5aee93... Merge branch 'constraint-list-model' into 'master'

(*) This commit already existed in another branch; no separate mail sent