Move schedule viewing to separate widget.

Now there's only SchedulePerDayView widget implemented, planning more widgets.
Implement basic drag-and-drop schedule constructor.

Drag and drop from subjects, instructors into schedule.
This piece of code is quite a bit messy. I need to refactor
it as quickly as i can.
Fixes for schedule [de]serialization.

Group numbers are framed quotes now.
If there's no schedules for certain weektype - it's not on the file.
Pair params are framed with square brackets now.
Implement scheduling features: save/open schedule to/from file.