Add ability to take attendance for past dates
Add ability to take attendance for past dates
Modified test based on pull request feedback
fix merge conflict
Revise tests using Timecop for dates
use optimized have_no_content [finishes #73931496]
Merge branch 'attendance'

Conflicts:
	app/controllers/instructor/attendance_sheets_controller.rb
	spec/features/instructors/attendance_spec.rb