Show logged in status on homescreen

[kumar-ish]

Currently the homescreen says Log In and Sign Up regardless of whether you already are or not. This should probably be changed to something like "Show committees" when logged in, and "Log in" when logged out, or be combined to one button saying "Log in/Sign up"

[MaxwellBo]

I think keeping the buttons seperate is good because it provides a good funnel for both new users and pre-existing users (even if they go to the same location).

But I agree, we could replace both if we have a non-anonymous auth context. This should be a pretty easy fix, with a Firebase auth hook.