Model changes for multiple Roles

Remove columns employees.role, users.role
Add columns employees.job_title, employees.agma_artist, users.superadmin
Add Permissions model
Update EmployeeForm with Employee changes
Update Signup form with Employee - change role to job_title
Add Seed data for UserRoles
Add CanCan

Add CanCan
Add authorization to all controllers
Add multiple roles to User model
Update page header views
Updated seed data for UserRoles
Merge branch 'cancan'