Not save empty classcard
Remove Enter as edit command
Add Group and ClassTime to ClassRecord
Reorganize classes
Create abstract ClassesTable class with type parameter
..
Create abstract ClassesTable and its child GroupClasses
Serialize without ClassesTables.
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
Feature: Colored border of warning and conflict card
..
BugFix: serialization/deserialization.
Merge branch 'exp' of https://github.com/Alllex/Schedule into exp
Add: fast year adding and removing
Add: forbid removing last year
Merge branch 'exp' of https://github.com/Alllex/Schedule into exp
BugFix: refactoring didn't work in xaml
Add: Group adding and removing via delegates