Move all source files to src/clj(s); update project.clj.

This paves the way for separate src and test folders; in fact, an
inactive test build is in project.clj now.
Call app entry point from index.html script block.
Add test database; remove db-* prefixes in db namespace.

To set up the test database, create a blank database named
`raiseyourgame-test`, then run `psql raiseyourgame-test <
raiseyourgame-test.sql`. Simple as that!

To run the server using the test database, set the `DB` environment
variable to "test". This value should match one of the top-level keys in
database.edn.

Automated functional testing would be a nice next step, but we can worry
about that later.
Initial setup and proof of concept for functional JS testing.
Ensure that CLJS start function is exported.
Provide force-pause function for testing teardown.

In the process, I rewired player state change to use async/publish and
async/subscribe. I was surprised how easy such a seemingly large change
was.
Test home page rendering; improve teardown; test helpers.