Added X11/Hirocoin support

Added X11 support via Evan Duffield's xcoin-hash Python module, along with a policy for X11 chains.

Also added specific settings for Hirocoin as an example X11 coin. This required changing the DB column chain_code3 to CHAR(4), as Hirocoin has been changed to "HIRO". Not sure if this will require a search and replace of code3 to code4?