Partly rewritten TGitCache logic to improve accuracy

Reduced flickering of icons and better support for "unversioned files mark parent as modified".

Signed-off-by: Sven Strickroth <email@cs-ware.de>
TGitCache: Allow to propagate subrepository stati to parent folders

Signed-off-by: Sven Strickroth <email@cs-ware.de>