Include symbols in main typeahead

Summary:

• Include symbols in main typeahead results.
• Simplify the symbol query a bit and extend PhabricatorOffsetPagedQuery. There was some stuff around language ranking that I got rid of, I think the theory there was that mapping file extensions to languages might not work in general but I think it works fine in practice, and we have more config stuff now around guessing languages and getting the mappings right.
• Make it easier to debug the typeahead by showing the results in page format for non-ajax requests.
• When we have too many results, show only the top few of each type.

Depends on D3116, D3117

Test Plan: Used typeahead, got symbols in results. Hit endpoint with non-ajax, got useful debug view.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3118