Make search more consistent

This commit limits search to 'title', 'name' and 'email' fields - I believe this is better for now, because we are only showing these three fields in the search results. Showing hits from other fields only confuses the user because there is no way to tell why a certain hit showed up in the results. Limiting the search fields also enables us to sort the results making the search results seem less random.

This should also improve performance because we reduce the number of rows (and the amount of text) that needs to be checked. It also reduces the amount of work needed in do_search function (less results to filter out).

I have tested these changes thoroughly on my local machine and search feels a lot better, but please let me know if I missed anything.

Stories: 
https://www.pivotaltracker.com/story/show/63643760
https://www.pivotaltracker.com/story/show/61900004
https://www.pivotaltracker.com/story/show/67787574
https://www.pivotaltracker.com/story/show/53787661
https://www.pivotaltracker.com/story/show/60379282
https://www.pivotaltracker.com/story/show/56420526