Merge pull request #12 from WonderCsabo/master

Removed accidental .DS_Store file
New task mailer
Minor changes
Add Friendly ID to students.
Merge pull request #13 from helenalissenko/master

New Task Mailer
Merge pull request #14 from Ki-csen/master

Add Friendly ID to students.
Config
Added devise_invitable for Students
merged upstream changes