Pagerduty module additions

Tested with test_module and in a production environment. 

Added:
- ability to end maintenance windows with the 'stopped' state
- token auth (requester_id defaults to user)
- set minutes when creating a maintenance
- lookups for service ID and user ID
- implemented 'changed' logic
- added error handling to PD API calls

Changed:
- 'user' can now be name, email or ID
- 'service' can now be name or ID
- deprecated redundant 'running' state, merely an alias to 'started'