Rewrite EntityResource to use new query methods

ActiveRecord.all and hash-based options are deprecated, which makes
logic like the original hard to replicate.

It also had a bit of a logic error.  Once the pages method was called,
it'd be cached in the @pages variable and never re-ran even if the query
options were changed.  The excerpts method would also be affected.
Entity model tests
Use sunspot matchers for testing solr queries
Run unit test when fixture is modified.  Cleanup
DC_CONFIG -> DC::CONFIG

Since the Rails app is DC, it seems inappropriate for the
constant to be DC::DC_CONFIG.  This moves it to DC::CONFIG and includes
required modules under lib.
Specify :smtp only for production mailer.

Otherwise tests attempt to send mail.