add statistics feature to count max nbr students in 2h slot

[bjornregnell]

add a new url sigrid/stat that displays statistics of how many students each room had during 8-10, 10-12, 13-15, 15-17 each slot (perhaps let sigrid know about the schedule in the course?).

[bjornregnell]

idea of implementation: record for each known room for each 2h slot for each date that Sigrid is active in week days (Monday-Friday) the maximum number of students in each slot and save to disk. The route sigrid/stat displays what is saved to disk.