DG DH; made acts_as_api play nice with backbonejs.  comments are semi-functional; stream elements use the StreamElement js widget (for now).

add acts_as_api to the models directly for now.  the 'root node' problem (posts : {}) breaks backbone.  wip

The old implementation which uses Post.where causes

  undefined method `abstract_class?' for Object:Class

in spec/controllers/posts_controller_spec.rb.  Not sure whether that's a problem
with Rails, or rspec, or what.

DH DG; made privacy page; can now unblock a user; users are actually being blockocked in ajaxed streams

fixed scoping stuff

wip oembed refactor.  still need to make a oembed_helper, and move some tests to their new home, but e but we are looking preeeetttttyyyy good.

Leaving the #order call in #last_three_comments caused the generated SQL to
have two conflicting ORDER BY components, which caused the query to return
invalid results.  I removed the problem by removing #last_three_comments which
I consider a premature optimization.

added tag follow feature, mention page feature.  is now pretty easy to add new types of streams, but some more refactoring could make it even nicer

put receiving in a transaction, to prevent the crazy duplicate index errors and hopefully fix federation visibility.