Finished TexturePack Download Code.

Implemeneted auto-updating for texture packs on mod pack launch with
previous texture version installed.
Enabled texture pack pane.
Check if texture pack exists for mod pack version prior to attempting
download/installation.
Added file exists method to DownloadUtils for non-static files on the
repo.
Removed link printing to console.
Overloaded the getPackVer method in settings to allow custom dir
passing.