Define how contributions are credited

[adamltyson]

The @all-contributors bot provides a nice and easy to way to ensure everyone is credited for their work on BrainGlobe tools. This would include direct code contributors, but also those who have contributed to previous generations of the tools, contributed data, or tested the software.

I've raised a PR to https://github.com/brainglobe/imio to add the tooling, and this should be added to every repo.

all-contributors provides a lot of options. We should decide on what level of contribution determines whether someone "gets" the emoji. I think to make things simple, if anyone contributes anything at all to any of these themes, they get added to the list, and get the relevant emoji. The only downside I can see is that some people may have 10+ emojis next to their name, but that seems fine.

[adamltyson]

Contributors have now been added to the website. We decided to not have types of contributions, and have a single list of everyone who has contributed.

There's an issue open about improving this - brainglobe/brainglobe.github.io#62