CHANGED: cleaned MCInstaller

 * added downloadToFile (URL url, File file, int attempts)
 * adapt MCInstaller to use new downloadToFile()
FIXED: ThirdpartyPack server download

 * NEw GUI broke server download. Now fixed
FIXED: fixed #792: missing logo/image

 * fixed uncatched exception if image pointed in XML does not
   exist in FTB repo
 * uses hardcoded default image
Merge pull request #801 from jikuja/fixes_for_v1.4.0

Fixes for v1.4.0