Tweaks to WeatherStation.py.  Now populates the safe property rather than returning a boolean.  Also renamed is_safe method to check_conditions.
Started laying out camera simulator architecture.
* Renamed brand to type since there may be multiple types with the same brand in some cases.
* Changed default values of type to be 'Simulator'
* Edits to section on weather to match current status of weather module.
* Cleaned up heartbeat method to use with format
* Removed hard coding of -12 degree twilight horizon and made it an option with a default of -12 degrees.
Merge branch 'develop' of https://github.com/panoptes/POCS into develop

Conflicts:
	panoptes/observatory.py