Remove code duplication using abstract constructor for FetLifeContent class.
Add skeletal `FetLifeGroup` class, begin parsing Groups data from profiles.
Parse out other forms of content from the profile lists, too.
Change class member declarations to PHP5 style.
Instantiate objects with a FetLifeUser object, too.
Remove redundantly redcared FetLifeContent class `id` members.
Fix bug where event page parsing failed to extract the event's title.
Correctly check for these elements existence before use.
Deprecate `created_by` in favor of `creator` in FetLifeEvent objects.
Add `getParticipants()` method for FetLifeEvents to get all RSVP lists.