Queries should error if no prefix is provided.

Conflicts:
	server/server_query_handlers_test.go
Fixes prefix override.
Fixes prefix in json for queries.

Conflicts:
	server/server_query_handlers_test.go
Fixes query count test.
Merge pull request #179 from Shopify/dupsort_fix_prefix_query

Dupsort: fix prefix queries to support passing as query param or in json