Use .desktop's over filelist

[Mia-Rain]

Looking over this in an attempt to use it outside of crew (since as far as ik there is not replacement for this exact project) it seems nearly everything references the .filelist of arg[1]/#{pkg} -- this seems odd to me, it literally calls grep just to find the .desktop when they all are held in a known location (#{CREW_PREFIX}/share/applications/) -- just search the folder for arg[1]/#{pkg} or use an exact file path when it's given

additionally it looks like the .filelist is read to find the icon file -- again why? The .desktop file has a variable called Icon which states the icon name/prefix in #{CREW_PREFIX}/share/icons/

there is no direct requirement for crew here.

[Mia-Rain]

additionally doing this would fix #7

[Tabby]

To add to this, it doesn't seem possible to supply your own .desktop file for packages that don't have one (e.g. codium) because even if you create one in #{CREW_PREFIX}/share/applications, crew-launcher refuses to find it when you run crew-launcher add <pkg>, and if you try to add the .desktop file specifically it gives the error "Package ./foo.desktop isn't installed."

This would also be fixed by using the standard .desktop location (falling back to the filelist if need be)