Port FolderView to ContainmentLayoutManager plugin
functionality doesn't change, minimal ui changes and solves some issues related to plasmoids resizing and screen resolution changes: now applets stay with the same distance to their nearest border or center.
Touch manipulation also works better as resize handles and applet handle buttons become bigger when interacting with touch, also pinch-based resizing is now possible
Depends on D22034
running since a while, seems to be stable and some of long standing bugs seem to be solved.
now resizing gets correctly blocked when it collides with another applet and changing temporarly screen resolution doesn't mess up the layout that much
Config migration script also works correctly
Reviewed By: ngraham
Subscribers: davidedmundson, ngraham, plasma-devel
Differential Revision: https://phabricator.kde.org/D22035