Sourcecred Contributor Wall Should be Configurable

[nothingismagick]

I just raised this issue at sfosc/sfosc#136 - but to summarize, the wall of contributors is not optional, and might misconstrue affiliation or acceptance of the project. An example might be someone who is totally opposed to something coming to express their discontent and being very vocal about it. Technically this is a contribution, but maybe they don't want to be part of it.

I think that the wall should be optionally whitelistable.