#57845848 Added SurveyInvitation.
Have Survey accepts_nested_attributes_for them, and SurveyController allow passing them as a comma separated list.
Use association for User/SurveyInvitation relation
Render flash in application layout
Strip whitespace around email addresses, which sneak in easily when entering a comma separated list
#57845848 Added SurveyInvitationsController.
Allow a SurveyInvitation to be accepted or declined.