[gtk] (7 commits) ...Merge branch 'columnview-1' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  e23baa5... inspector: Add columns to the object tree (*)
  0470078... inspector: Use a column view for properties (*)
  42d26b4... inspector: Use a column view for the resource list (*)
  23bc38e... inspector: Make the resource list sortable (*)
  0d9873d... inspector: Use a column view for actions (*)
  2a9d2cc... inspector: Touch up list styling (*)
  9335388... Merge branch 'columnview-1' into 'master'

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