Add username generator

[jayvdb]

A library + CLI

https://github.com/awesmubarak/username_generator_cli

Two good tools, but not a library

https://github.com/dorzel/username-generator https://github.com/vardrop/gen-pkmn-name

Two online tools which could be used for UI ideas.

• LassPass (choose "easy to read"!), or
• https://username-generator.appspot.com/ (https://github.com/PurpleBooth/username-generator)

[jayvdb]

https://pypi.org/project/username-validator/ would be quite useful as well to reject bad suggestions. Or that could be a followup task.

[jayvdb]

Note that this task will mean we can remove a huge part of https://github.com/coala/coala/wiki/Google-Code-in-username