Remove bitrotted programs for Android, iOS, Playbook and Qt

Noone has worked on them for ages, and it seems noone will in the near future. So let's remove the dead code from the active development branch. It can be always restored from history if needed.

Advantages:
* greps throught the whole codebase will not accidentally pickup stuff from there
* less directories cluttering the project view in the IDE
* no longer possibly demotivated by always being reminded there is lots of dead code around that needs to be worked on again

Any best practices known how to tag the last version which has the latest version of these bitrotted subprojects, in case somebody wants to continue again? Create a tag/branch? Or should people do rely on searching the commit message?