This makes the behavior of the app drawer a bit more familiar and
slightly more similar to Android for now:
* The drawer always contains every application
* Applications are always alphabetically ordered
* The drawer opens completely, not staying stuck in "in between" states
* is possible to drag more copies of a single app on the homescreen/favorites
* possible to remove an icon from the homescreen or favorites
Two things have been prepared in there (but are material for 5.22 only,
so not finished)
* Things have been reordered such in a way that makes easy for most of
the qml files to become components to make easy for people to build
their own customized homescreen
* basic infrastructure is there to allow for multiple horizontal pages
scroll, though not implemented yet as needs changes to plasma-workspace
layouting code beforehand
the application list is only used in that containment for now: don't
create an extra qml import just for that, but put it into the c++
applet for the homescreen instead to make sure nobody else
uses it at least until we are really sure is needed elsewhere
