fix the seeds
fix leave button issue and styling
add membership polymorphism
Make it truly possible to join groups as student or coach.

* Added two buttons to group#show
* Add hidden type fields to buttons
* Added source to has_many relationship because the error message
  said so
have people instead of students and coaches aka delete all the things
fix the specs
update seeds
Display student or coach in email when signing up
Merge pull request #187 from rubycorns/insanity-branch

Insanity branch