getlantern/lantern#1622 Lazily creating user on invited check

Remove isInvited/inviteIfNecessary, remove this call to it and the first branch of this if statement, and replace it with a call to createInvitee() before what used to be the 'else' branch of the if.

I'd also rename createInvitee to createUserIfNecessary, because these are not really invitees, but this is just a nit.