[gnome-shell] (16 commits) ...appDisplay: Add additional view showing frequently used apps

[Florian Müllner <fmuellner src gnome org>]

Summary of changes:

  77d8ff3... appDisplay: Remove categories (*)
  2658754... appDisplay: Merge AppIcon and AppWellIcon (*)
  c9e2f16... appDisplay: Merge AllAppDisplay and ViewByCategories (*)
  4f8f79a... appDisplay: Remove unused variables (*)
  f21b820... messageTray: Move makeCloseButton() into Util (*)
  9758029... appDisplay: Make _loadCategory() a utility function (*)
  2fbd9b9... appDisplay: Set a maximum column number (*)
  426b227... appDisplay: Make AlphabeticalView an abstract base class of (*)
  25d8deb... appDisplay: Add intermediate stack widget to hold folder po (*)
  6e3e2d9... appDisplay: Add new FolderIcon class (*)
  65f9649... appDisplay: Separate app loading from filling the grid (*)
  6a1b341... appDisplay: Add AllView.addFolder() method (*)
  e3c9c46... appDisplay: Create AppFolderIcons for selected categories (*)
  6628214... appDisplay: Make folder popups "view-modal" (*)
  10e16cc... shell-app-usage: Remove unused parameter (*)
  b75fc2b... appDisplay: Add additional view showing frequently used app (*)

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