Add specs for Manager permissions
Add permissions for Staffers, Riders, Managers
add Assignment model, spec for Shift requests
add routes and permissions for Assignments
Add assignment index to restaurant profile page, Shifts#index
add Assignment partials to Shifts#index, add Shifts#index partial to Rider homepage
Add Assignments#new (with 3 view variations based on caller path)
Add Assignments#edit
Update validations on Restaurant model (staffer creating not required to enter all fields, manager editing does)
fix restaurant request specs
Revise Shifts#index, Restaurants#indes, and nav header to enforce permissions