Most notably:
* Use the much more narrow UserIdentity interface where possible.
* Make array type hints in PHPDocs as specific as possible.
Change-Id: Id189da4028b7874909277881dcf6539169dd13b6
The test doesn't need the database, but it's currently trying to use it.
Mock all services used by EchoDbFactory to avoid that (the Factory
cannot be mocked directly because it's created with a static method and
not injected).
Change-Id: I359489ed3f8de6e868a590d5c7c02f81f0a2049d
