Fixed bool bug and add comments to clarify
RM7213 Added IPPolicyCIDR.{first_ip, last_ip}

* Added addition of columns alembic migration.
* Added population of columns alembic migration.
* Added API code to populate columns on ip_policy_{create, update}.
* Re-wrote ip_availability script based on added, populated columns,
  vastly improved runtime performance by decreasing number of SQL
  queries.