Allow gold tier users to send silver invites

[neilsarkar]

Closes #91

So, unfortunately this is currently untestable unless you wait 24 hours and then hit the promoter endpoint. If we do end up delaying gold acceptance, we should provide a way to override that in development. /promoter takes an argument of time that would let us let in anyone waiting to be auto-approved in development. I wonder if we should have our own "Debug" menu in the client as I'm sure this won't be the last time we need to do something like this...lemme know your thoughts

[benjaminben]

Love the idea of a debug menu in the client