Add mod removal to launcher

This will 'clean' the mods directory every update, but will
leave directories intact. This should fix mod updates with different
names.

Signed-off-by: Tristen Allen <spyboticsguy@gmail.com>
Changed the libraries to not redownload if we have no md5

Signed-off-by: Dalton Pelc <daltonjpelc@gmail.com>