improve search

[bcoe]

• make it so you can paginate search.
• make it so you can sort search based on various criteria.
• have a sane default for sorting search, e.g., alphabetical + bpm + rank.

[DeviaVir]

ref. #19, #11, #10

[bcoe]

I've finished implementing a first pass at an improved search-API, see https://github.com/bcoe/record-crate/pull/24 (of particular interest, I needed to add headers to Polymer's core-ajax requests). Here's how the new search API works:

• a search response will now have page, page_size, and total, populated, these values can be used to paginate search results.
• pass the key page in a search request, to get the next page of results; searches start at page 0.
• I've changed the default sort for search, so that _score is now taken into account automatically. This will result in keyword searches returning more logical results, once a search-box is added.
• I've added an abstraction layer on top of ElasticSearch's sorting DSL., to sort by different values simply pass an array of this form:
  • [['bpm', 'desc'], ['artist', 'desc']].

Let me know if you have any questions @DeviaVir :+1: