Create abstract ClassesTable and its child GroupClasses
Merge branch 'exp' of https://github.com/Lozov-Petr/Schedule into Lozov-Petr-exp

Conflicts:
	SEE/Editor/Repository/ScheduleRepository.cs
Comment import-export while not working
BugFix: classes table, classes initialization
..
BugFix: serialization/deserialization.
Merge branch 'exp' of https://github.com/Alllex/Schedule into exp