Add Buddyboss theme support

[ZiadJ]

I've already posted an issue in the official repository for a similar plugin a while ago but the developers there have other priorities right now apparently so I thought I'd try my luck here instead and wouldn't mind sharing the files for the theme itself with anyone willing to work on it if that can help.

Thanks for developing this plugin by the way. I'm planning to use it for implementing a direct democracy eventually and it's about the best one I've found so far for that purpose.