Finished implementing main methods for SQL extension

Finished supporting all the main methods for the SQL extension and ported all the remaining relevant tests.

The SQL extension now supports: GET, POST, PUT, PATCH, DELETE
All these methods come with the relevant integration tests that cover most of the scenarios of the Mongo equivalent. I have also added some basic unit tests for some of the components of the extension, more to come.

Notably the biggest differences are:
- No support for Mongo query syntax
- No support for lists or dicts in POST, PUT and PATCH as they don't make much sense in a SQL db
- No support for Mongo write concern in POST, PUT, PATCH

TODO:
- Clean up and refactoring of tests to remove duplicate code
- Support for Eve custom `ID_FIELD`, `DATE_CREATED` and `LAST_UPDATED` fields
- Support for `find_one_raw` and `find_list_of_ids`