LDEV-1670 unordered lessons used to be appended in a non-guaranteed order (HashMap backed collection); switched to TreeMap, and prepend unordered lessons so that new lessons appear at the top of the list by default.
lams_central shouldn't have dependency in lams_learning - moving method from LearnerService to LessonService in lams_common, as a result also moving Index*Beans to lams_common
LDEV-1483 sort lessons on 'all my lessons' according to the order set by a teacher from the 'my groups' page. also fixed bug with subgroups appearing more than once if there were more than one lesson in it.