Added rename

So I added a rename function into gobby.
It mostly works, except that there is a signal needed, to let know when a node has been renamed, so we can change the TitleBar and TabLabel text accordingly.
One way would be to connect a signal in SessionView.cpp, and have inf-browser.c send the signal through the corresponding InfSession. But there might be some other better way.
These two changes do not belong into this commit. I'm not against clarifying comments in general, but these should be in a separate commit.