#4 Add support for private clubs

[Alf Mikula]

Add support for private clubs. Club administrators should be responsible for accepting or rejecting membership requests, as well as inviting new members.

Club membership should be displayed on users' profiles. Also, sites should be able to be configured by club members to be visible only to members of one of their own clubs, and these locations would not be visible to other users, nor would game offers for games at these locations be visible to non-members. These private locations could be used for people starting new Go clubs and meeting, eg., in people's homes, or for clubs at corporate locations (ie, a particular conference room at Corporation XYZ).

Members-only locations should be clearly marked when they are displayed in search results.