Allow Colonies to be marked public or private


Individual Colonies should be able to be marked/flagged public or private to indicate whether they are meant for a specific group of people who know each other already (private), or meant to be public: open to anyone who aligns with the Colony description (see separate feature request for that).

This flag would then control things like whether the Colony description should be indexed and shared broadly, etc.

A further refinement of this would be to store something similar to a robots.txt document that would specify which aspects of the Colony should be searchable and indexed for those Colonies that are marked public.