Merge pull request #1 from Harvard-University-iCommons/develop

Make corresponding mixin for LTI roles being required.  Remove GroupRequ...
Merge branch 'develop'

* develop:
  moved the code that stashes the LTI launch params to be after login(); fixes issue with masquerading in Canvas
changes failure on request.session.get('LTI_LAUNCH', None) returning None from an AttributeError to an ImproperlyConfigured exception
refactors common logic from decorators and mixins into new verification module
in doing so, applies the improved error message to mixins as well (previous commit only applied it to decorators)
Merge branch 'develop' of github.com:Harvard-University-iCommons/django-auth-lti into feature/configuration_check

Conflicts:
	django_auth_lti/mixins.py
adds tests to verification function
slight code reduction
adds two tests and redoes config check to test for type rather than just presence
Merge pull request #7 from penzance/feature/configuration_check

Pulls out common logic from decorator and mixin, and adds check for configuration