Abandoning cool mongo driver thing.

I'll throw that in a separate project. It works though. A great proof of
concept. With the null driver, test speeds are around 0.1 seconds
instead of 3s. Improvement of 3 seconds is nice.
Fixes a Person model test.

The test recursively attempted to use a function it might call. The new
method of testing this is far safer and easier to understand.
Adds functionality to Activity model.

Adds object= and object functions to convenient make use of object_uid
and object_type.

Fixes find_or_create_by_uid! to use first instead of find.

Allows create!/create to be given no arguments.

Activity::discover! will not rediscover an Activity that is trivially
found locally.

Adds #parts_of_speech method to give the bare components of an Activity
without creating a sentence.

Preping to move #human_description to a lib or presenter.