Refactor so that new watchers/auditors are easier to add

This pulls a lot of code from ```security_monkey/__init__.py``` into the ```security_monkey/scheduler.py```. Consider that maintenance.

This also creates ```security_monkey/monitors.py```. A monitor is a watcher and the associated auditor. When adding new watcher/auditor pairs, simply add them to the dict in ```security_monkey/monitors.py``` to get them setup with ```manage.py```, reporters, and alerters.