Desktopfile

Linux desktops like gnome and kde have a similar format for desktop entries, describing how a particular program is to be launched or presented (icons, tooltips, etc) in the menus and the mime types it supports.

The full specification of destop files is available here: http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html

This PR contains basically the desktop file. Although the file could be installed with python setup.py install, it would complicate the logic of the installation, as we had to check: "is this linux?, is this GNOME?, is this KDE?, do we have the program desktop-file-install?" So I haven't tried implemented it.

The desktop file can be manually installed by copying it to $HOME/.local/share/applications.