custom required levels for each defined group, calendar views, colors

lectures/admin.py

...es/migrations/0023_alter_lecturelector_avatar_and_more.py

...024_remove_lecture_groups_remove_lecture_type_and_more.py

.../migrations/0025_alter_lecturegrouptype_group_and_more.py

lectures/models.py

lectures/templates/lectures/includes/lecture.html

lectures/templates/lectures/includes/lecture_type_color.html

lectures/templates/lectures/view_group_lectures.html

lectures/templates/lectures/view_lecture.html

lectures/templatetags/lecture_group_types.py

lectures/views.py

shared/templates/shared/includes/base.html