Made the cache folder always be created before anything tries to use it,
just in case.

Signed-off-by: Dalton Pelc <daltonjpelc@gmail.com>
Made failed downloads stop the launching of a pack, display an error
message, and then reset the form to allow for playing a different pack.

Signed-off-by: Dalton Pelc <daltonjpelc@gmail.com>
Merge branch 'master' of https://github.com/TechnicPack/TechnicLauncher