Fix bango logout (bug 1105076,1105076,1049004)

* Use logged_in_user as the key for provider logouts. 
* Set the localStorage to a logout+timestamp when we logout (This causes the provider logout later at the point we know the provider).

r? @kumar303 @washort 
I don't think this is correct because it will always log people out. We only want to log people out if the email changes. The code to do a logout when emails change was already in place though, right? Could this be a Bango bug?