Per-activity favorites (Final, again?)

Summary:
The favourites are based on KAStats (already released version) and kactivitymanagerd master (to be released with the next Plasma release). It allows favourites to be set to all activities, or the user can choose which activities to show a specific favourite application on.

This change covers applications, files and contacts, other favourites are still based on the old model (now named SimpleFavoritesModel).

Test Plan:
Tested in Kicker, Dashboard and Kickoff the following:

Transitioning mechanism:

• load default favorites for the blank user
• load custom default favorites set in the plasmoidsetupscripts script for Kicker
• transition old results - when transitioning, merge the favourites from all launchers. The ordering for each launcher is kept separate (newly added items due to the merge go to the end)

Favorite manipulation:

• right-click add favorite to all activities
• right-click remove favorite from all activities
• right-click add favorite to specific activity (current)
• right-click remove favorite from specific activity (current)
• right-click add favorite to specific activity (not current)
• right-click remove favorite from specific activity (not current)
• right-click move from all to specific
• right-click move from specific to all
• right-click move from one activity to another
• dnd reorder items in the model (up)
• dnd reorder items in the model (down)
• dnd add to favorites at a specific position

Other:

• launch the application
• ordering persists after restart
• ordering from the previous is kept on the activity that has no ordering

Reviewers: mart, hein

Reviewed By: hein

Subscribers: Zren, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D3805