Update schema

New schema has:
- prepositions for sentences, used in describing search results
- A document_noun for describing search results
- single-select or multi-select for lists of options
- an 'all' value for case_state
Merge pull request #14 from alphagov/update-schema

Update schema
Symbolize parameter keys in Sinatra adapter
Misc fixups
Keyword search over all document fields

* Extract query building from search repository
* Add text search capability