Add a flash message to inform user they have been successfully assigned to a group.
Add a flash message to inform user they have been successfully assigned
to a group.

nyc-mud-turtles-2015/nghborly,nyc-mud-turtles-2015/nghborly,kimchanyoung/nghborly,kimchanyoung/nghborly,nyc-mud-turtles-2015/nghborly,kimchanyoung/nghborly