Fix a bug when an overlay isn't in the remote list

If the overlay isn't in the remote list, it obviously isn't a different
type, nor has its URL changed, so just init those to False so we can
sync the overlay without hitting UnboundLocalError.
Merge pull request #19 from dwfreed/patch-1

Fix a bug when an overlay isn't in the remote list
module.py: Adds modular plugin system