Core/maps: Change several types to BIGINT to stop overflows in havoc.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit cbbbaf159d325a6e3b3a2192e5ac2c1e6f009fc4)
merlin.cfg: Add a note about sharing to Scans.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
merlin.cfg: Add arthururls section.
Arthur/settings.py: Use new arthururls section.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
merlin.cfg: Add all alturls (commented out) to default config.

Signed-off-by: Martin Stone <martin@d7415.co.uk>