Fix for 404 when empty JABBER_DOMAIN set

* Properly handle empty (rather than merely missing) JABBER_DOMAIN
  configuration variable.
Merge branch 'master' of github.com:Stanford-Online/class2go into jrbl-empty-tps-report-domain-fix

Conflicts:
	main/courses/views.py
Remove confusing config from database_example.py

* Having sample chat config in database_example is a little confusing
  for people, so let's just not put it in there until we're sure
  everything works on our setup.
Merge pull request #2427 from Stanford-Online/jrbl-empty-tps-report-domain-fix

Fix for 404 when empty JABBER_DOMAIN set