Add in custom events

In the beginning, these may not be completely customizable, but the following custom events such be available for install:
- User registration
- User login
- New topic
- New reply
- PM submit
- Search
- Popup view (notification bar, profile widgets, etc.)

These should be created as data hooks, and call `$registry->TP_GoogleAnalytics->_trackEvent( ... )` with their appropriate information
