Twilio updates

Added a check for LVC membership before making phone calls. Moved code which makes the phone calls into its own function. Moved Twilio account SID, auth token, and URL hashes into a secret settings file (encrypted and deployed via Puppet).  Also added a help text note on the Create Contact page.

See merge request !1

Implemented new VOEvent parameters and allowed preliminary VOEvents to include skymaps (although they aren't required to).

a plot of recent events on the landing page. The latter is
only shown if settings.SHOW_RECENT_EVENTS_ON_HOME is True.
Setting it to false for now, since we are not in a run.

Also added Reed's tutorial on LVAlert.