Use more rememberable autogenerated user names

Distinguishing between Guest-zGbKWstN and Guest-8hwNKSYa is difficult. More natural names would be better. Docker [came up](https://github.com/docker/docker/blob/master/pkg/namesgenerator/names-generator.go) with a great idea: a list of names (scientists in their case) and adjectives, and then mix them up randomly. So you could get boring_einstein or sleepy_galileo or other combinations.

I think groovebasin could use a similar scheme, but using musicians instead of scientists. 30 names and 30 adjectives yield 900 random names, which should be enough for everybody (tm).