added sign in part

fixed bugs like making a new event if refresh is clicked, events page
now only shows events for today. Bug still left: only events that are
contained within today are shown. It needs to be any event that has at
least some amount of time today. Also events that span multiple days
will never be shown.
external event sign in

still have to make links in the navbar, fix minor bugs like signing in
more than once, showing errors when trying to sign in to a nonexistent
event