Admin::API - Split into two controllers

[ewlarson]

Currently, in api_controller.rb, we're not automatically sending all controller configured facets to Solr. Instead, we're using Solr's solrconfig.xml file to define the list of facets for basic search, and we're using the controller file to define the list of facets for advanced search, many of which have extremely large limit options set.

We should split this one overworked controller into two separate controllers:

1. Basic Search / api_basic_search_controller.rb
2. Advanced Search / api_advanced_search_controller.rb

This would allow us to NOT need Solr config changes to update the list of facets for basic search. It would also greatly simplify the configuration of these two files, making "how this works" much easier to understand for other developers.