Calendar: Add entity selection

[Gaby Roch]

Now /calendar command display user timetable.
Can add an args for select entity type ((default) self calendar, room, professor, lesson or other student calendar)

For get ICS for specific type, change the call of get_timetable_ics() and set type args to good value

[Gaby Roch]

Example :
/calendar [<date>] : self calendar
/calendar s[tudent] <name> [<date>] : calendar for student
/calendar r[oom] <name> [<date>] : calendar for room
/calendar p[rofessor] <name|abr> [<date>] : calendar for professor or
/calendar l[esson] <name> [<date>] : calendar for a course (ANA-1-A) or a branch (ANA ou ANA-1)