Adding 'Thunar' to the title bar

I believe the removal of 'File Manager' from the titlebar in fffa7f2a was a good thing, as using a generic name rather than the application's name is wrong, but rather than simply eliminating it, it should have been replaced with 'Thunar'.

The reason why is that all other multi-window apps, follow the same format for the title bar of 'Document - App', like Mousepad, Chrome, Firefox, GIMP, LibreOffice, Virtualbox, etc. and to break from this pattern is bad UX.