Use PhantomJS; start/stop Selenium

[refs #66791650] [refs #59939212]
Do not .gitignore bin/ and lib/
Add one working UserAdminSpec

Note: a previous commit didn't work, because our root .gitignore ignored
lib/ and bin/. This is the first working integration test.
Ignore /assets/ requests; log more nicely
:s/Ok/NoContent for empty application/json.

This complies with HTTP specification.
Finish UserAdmin integration testing