add window title option

[lashkevi]

It would be convenient, if the user could choose the form of the main window title in the TS configuration: 1) the full path to the file, or just the filename, or the path relative the home (or any given) directory; 2) the filename or the session/project name (E.g. I regularly start simultaneously multiple instances of TS for multiple projects with several files each, and the project name is more important to me than the particular filename.)