One query multiple suggesters

Rewriting the /suggest query to contain multiple suggesters in one query rather than having one suggester per query and making multiple query calls in parallel. 

Adding queryMixer.json that contains information of each suggester (layers to query, precision, fuzziness etc) - plan is to possibly rip this out into its own module (upto discussion) but for now its nice to have it live in a separate json file instead of being buried in the code. (tests for queryMixer are included)

no separate controllers/tests for suggest_nearby. there is one suggest controller that accepts different queries (see app.js)