Added chat base classes and indexes.
Added chat base classes and indexes.

I think this is not being used unless diaspora native chat is
enabled.

Refs: #6

piraz/diasporapy,candango/diasporapy,piraz/podship,piraz/podship,piraz/podship,candango/diasporapy,piraz/diasporapy,piraz/diasporapy,candango/diasporapy