Add factory_boy and define initial factories

[werberger]

This resolves issue #104 (add development fixtures). Although a factory has not been defined for Activity

[werberger]

I think I've done it. Let me know if I should have done anything differently.

[werberger]

I ran isort and black which fixed up a number of things. Flake8 threw many errors (>150k), so assumed they are already known about. test coverage is 83%.

I hope that's everything. But if not, I guess it's all learning for future PRs.

[brylie]

@all-contributors please add @werberger for code

[allcontributors[bot]]

@brylie

I've put up a pull request to add @werberger! :tada: