Set up basic data structures + relationships for Student, Section, Attendance, Request
Added attendances association to Section and Student
Added basic validations for presence
Added TargetValidator
Added custom validations to Request and Attendance to make sure that Students don't attempt to sign up for multiple sessions of the same class or request a change to the same class
Added e-mail validation gem where relevant
Merge pull request #1 from shippy/data_structures

Data structures and validations!