Capability: Email all to conference attendees

* Functionality revealed to su's only
* New email page
* Acknowledges variability in `ConferenceAttendee` - code for both
current situation and possible later transition to using `User` fields
is included
* Extension for emails to selected attendees included
Merge remote-tracking branch 'james/master'

Conflicts:
	myrobogals/urls.py
Forum meets world