task/ta-167 -- Provide support for lats and longs in the Agent table

top/adp.py
* new methods sanitise_latitude() and sanitise_longitude() (as the
  name says)
* update the sanitise() method to include the lat/long sanitisation
  calls
* update the update() method to include the lat/long sanitisation calls

top/conf/top.conf
* enable the lat and long columns under the [adp_headers] section

top/table/agent.py
* update the agent schema to support new latitude and longitude columns