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).

{F1028047}

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