Every Mutex lock should now guaranteed to be released in a finally clause. Moved some common code in a new file. Adapted to renamings in tox.h.

ToxGlue.cs: <= InputHandling.cs, Popups.cs
- common functions for InputHandling.cs and Popups.cs

InputHandling.cs:
- added group commands

ToxInterface.cs:
- every WaitOne() -> function -> ReleaseMutex() sequence should now be guaranteed by a finally
- adjusted external function naming to additional underscores
Merge remote-tracking branch 'origin/master'