Move `{. => dom}/src`

[japgolly]

Currently the root project is .root and dom is .. It should be . and dom respectively.

[japgolly]

Doesn't matter, fine as is

[japgolly]

Actually I should do this.

1. Makes the project consistent within itself, and with most other projects
2. A user who opens sbt and runs test would be surprised to find that there are other modules whose tests didn't run

[japgolly]

I'll do this quickly now while the PR queue is empty