Implement virtual DebugSession::killDebuggerNow()
Once kdevelop!182 (merged) is merged into 5.6, this change will be necessary only in kdev-python master.
kdev-python compiles with this change. All 6 tests pass. Sorry, I haven't tested how this commit works, because I am not a python developer and have zero experience with kdev-python.
See the commit message for details.