add route, controller, and basic view for attendance statistics
remove unused method call from controller
add tardy boolean to attendance_record

Created a after validation hook that will mark an attendance record as
tardy if it is after the start time. Doing this will means we have records
of tardiness even if we change what the start time is.
fix bug by properly using travel_to
add graph showing number of students present each day
add methods to user to check number of on time attendances, tardies, and absences
add cohort_attendance_statistics model
add bar chart to show student attendance breakdown
change route for seeing attendance statistics to be nested through cohorts
add specs to ensure graphs render on attendace statistics pages
adjust styling on attendance graphs
fix test conflicts with number of absences

Calculating the number of absences is dependent on knowing how
many days have passed since the start of class. The original thought
was to only count days that have passed. This made calculating
attendances not work as planned. After further consideration, it
did make more sense to count the current day as well as the ones
that have passed.
remove routes for cohorts (to be added later)
clean up code for merging into master
Merge pull request #20 from epicodus/attendance-statistics

Attendance statistics