Use D-Bus to lock sessions and move "session locked" dialog (from KDevelop's main()) to kdevplatform

Review Request #105917 - Created Aug. 7, 2012 and submitted - Latest diff uploaded

Ivan Shapovalov
git master
1: Use D-Bus instead of lock-files to lock kdevplatform sessions.

2: Moved the lockfile remove dialog which currently resides in KDevelop's main() - and which is usable only when the session name is explicitly given to the application - to kdevplatform's SessionController, adjusting the dialog for "lockfile -> dbus" changes.
This allows to get rid of nasty non-informative error messages about a session being already used and replace them with code that does the following things:
1) Attempts a DBus call to make a running instance visible;
2) If it didn't succeed, shows a dialog window asking permission to retry, show session chooser dialog or quit;
3) Repeats the entire procedure if a newly-picked session is locked too.
This code is also used when one picks a session from "Sessions" menu, so a nasty error message has also been removed also from there.

Related change to KDevelop is here: .
Existing unit-tests + manual UI testing.