[IMPR] Some improvements for imagetransfer.py
[IMPR] Some improvements for imagetransfer.py

- add -tosite command
- improve option handling
- show all found files at once in a list
- add colored hints
- add a new method transfer_allowed which will be changed
  for solving T267535

Change-Id: I7256430241f64962e6f0740dbcea51018a299161

wikimedia/pywikibot-core,wikimedia/pywikibot-core