Support Notifications in the Facebook adapters

The Notifications support in the Facebook OpenGraph API is still in
beta, so this is likely to change at some point in the future.  In
particular, the paging API currently doesn't seem to work at all,
perhaps due to the "until" parameter being incorrectly formatted by
the Facebook backend.
Merge pull request #114 from chriadam/master

Support Notifications in the Facebook adapters
Merge pull request #115 from matthewvogt/self-contact

Expose the selfPerson without requiring a model instance
Allow filtering for 'online' contacts

Similarly to favorite filtering, return only contacts that are considered
to be online.  Using Sparql, this means they have an IM account whose
presence state is something other than offline.
Use enum sequencing to provide count of filter types
Do not include unknown presence status in the 'online' results