task/ta-npi-022-10 -- send failed comms notice email

nparcel/config.py
* patch the db_kwargs() and proxy_kwargs() methods so that it handle
  non-value int casts

nparcel/loader.py
* new method get_agent_details() which factors out the agent details
  extract
* updated the process() method so that it send an email notification
  to alert of comms errors

nparcel/loaderdaemon.py
* updated the start() method so that Loader initialisation supports
  the new failed_email option

nparcel/restemailer.py
* updated the create_comms() method signature to include an "err"
  argument to invoke the error template