Some applications won't start

[gdematos]

This issue can technically arise with any backend script, but Applications is the most problematic. Some applications specify a shell command as a start command, which fails currently with Nozzle.
Such applications include Steam, which starts up with the following command:

sh -c 'STEAM_FRAME_FORCE_CLOSE=1 steam' %U

EDIT: Also add support for starting an application in a terminal (Terminal=true)