Firebase housekeeping + test fix

Simplified the Firebase config structure.

Without the Mocha’s `done` callback it didn’t wait for the cleanup to
finish and went on to run the next test, which lead to garbage in the
database.
Moved instantiation of Firebase* classes from core main to its own main
Give up on the test-unit task

Having tests run under two different environments (Node and browser) was
getting tricky without substantial benefit.
This app is not an NPM module