#79 Improved window title

[Denis Auroux]

As submitted by Michael Walter on the mailing list on Dec 10 2014:

please see theattached trivial patch, which changes the window title from "Xournal - $filename" to "$filename - Xournal". In this way, truncated title bars still give useful information. This is in line with the behavior of many other well-known programs (e.g., Chrome, Firefox, Sublime Text, ...)