Ported to new ProjectTox-Core master branch

Ported the GUI Project to the new master branch of ProjectTox-Core.
Saved the state of the Messenger to a File called save.bak and loaded it on startup.
This means your private and public keys are stored in filesystem and reused in next programm session.
The class Starter has now a destructor which deletes the MainWindow instance and this deletes the instance of Core.
The class Core and Starter are refactored with the pimpl idiom.
Classes CUserId and CString seperated into own files.
The "evil hack" for emittings singals from ProjectTox-Core-callbacks was removed.
Now the new length of ClientID is used. The old was 64 characters, the new is 76 characters long.