Added first specs for search_terms.

This table is set up to capture search terms that people are using to explore the dataset. It will create unique entries based on the string they use to search and then track the how often that string has been used and what times.
Updated readme

Created migration and model for search_terms
Implemented the class method .update_or_create_search_term

It works fine in IRB but haven't figured out how to test it yet.

First stab at writing the spec for the above method.

Also updated schema to default the when array to an empty array
Created a spec that reasonably covers the creation of search_terms
Created an AJAX request to pass the search_term to the server

Sorted out the search_term controller

Added an appropriate route.

Tweaked the .update_or_create_search_term method
Merge pull request #20 from thomasgwatson/search_capture

Search capture