RFC: handle for activity switcher is always shown on top, even on top of apps

[Fania Bremmer]

This one is tricky... but I heard it often as a request from users, so I 
give it a try here.

** Proposed Change **
Show the handle for activity switcher always shown on top, even on top 
of apps, to make switching between activities easy.

** Reason For Change **
Quicker change to another activity, instead of going back to current 
activity and pull the handle there.
Usecase: I am editing a document, a client calls me and I try to open 
his file/details etc in the other activity.

** Implementation Details **
- handle is shown on top of every app -> problem: if important buttons 
of the app are displayed underneath the handle...