Reduce complexity for dev testing setup & update CONTRIBUTING.md

Currently, looking at our CONTRIBUTING.md, I see a lot of manual set up steps in order to run the test suite. This is a very unwelcoming first impression, and we could probably hide a lot of these details from the contributor anyways.

This set up process could be simplified by automating using docker, for example. I’m open to other suggestions also.

[mrhwick]

Bookshelf is built with knex plugged in as the module used for database connection and execution, which improves quality in bookshelf. This provides an opportunity for lowered coupling and increased cohesion in the sense that bookshelf no longer needs to concern itself with the manner in which database connection and execution occurs, as long as knex is well-tested and can be trusted to function as documented.

Subsequently, we can tighten up the focus (cohesion) of bookshelf as a library to spread only down to the API where knex will take over. It doesn’t need to concern itself with testing that knex reacts as expected with the correct inputs. I think this is a strong argument for removing the test scaffolding related to actually running a variety of databases and measuring the database effects of bookshelf code.

[mrhwick]

Bookshelf can expose the knex query builder without implementing or verifying any of that functionality itself.

That means that the knex library can be tested independently to provide verification and bookshelf does not need to concern itself with guaranteeing that knex’s functionality is correct. Knex should provide those guarantees, and bookshelf is not made any less reliable by proxying those guarantees out to its users.