* Added support for Apache Drill datasource
* Improvements in `Drill` query runner and minor refactoring
1. Drill query runner now inherits from `BaseHTTPQueryRunner`, because they both have a lot of common code.
2. `BaseHTTPQueryRunner.get_response` method now accepts `http_method` argument (original implementation was only capable of sending `GET` HTTP requests).
3. Added `order` to `BaseHTTPRequestRunner` configuration schema to fix order of UI elements based on the schema.
4. Eliminated duplicate method `_guess_type` in `GoogleSpreadsheet`, `Results` and `Drill` query runners, moved `guess_type` to `redash.query_runner`.
5. Removed tests for `_guess_type` in `GoogleSpreadsheet`, `Results` and `Drill` query runners, merged them into single test case and moved to `tests.query_runner.test_utils`.
6. Various minor changes (code style, imports, etc).
