Private variable name should be camelCase not _PascalCase

Also make AllClasses immutable and add classRoomSlots
Some more name refactoring
Add struct Room and struct TimeSlot
Manager also manages timeslots

- Add availablRooms
- Add availableTimeSlots
- Add RegisterClassRoomSlot()
Refactoring
Start rewriting Manager
Remove TimeTable and Room from Class
Initial Manager interface

Just the bare minimum to get started
Simple constructor for Manager
Implement GetStudentById and GetClassById
Manager: Formatting and encapsulation
Implement the rest of Manager
Remove previous adhoc tests in Main
Documentation
Simple test case in Main
Minor refactors