Download Statistics & Bugs

Adds download statistics : time taken, images downloaded.
Can now take bad filename input without crashing.
Added file replacement conflict parameter for batch scripts so it
doesn't get stuck asking the user.
Basis for resolving zoomify uris from regular html pages is setup but
still not implemented.
Noted a very rare special case in which the max zoom level was
incorrectly calculated and created a hack solution of trying a lower
zoom level instead of tweaking the algorithm.