Run JavaScript tests in semi-random order

To reduce unintended dependencies between tests and find the cause of transient failures more easily, we should consider running the JavaScript tests in semi-random order. Jasmine has a --random option which we can pass to it via the karma configuration.

It is probably a good idea to also set the randomization seed to the current commit hash. That way the test order keeps the same for a certain commit and allows investigating failures.

To the best of my knowledge, the RSpec tests already follow that approach.