Delete useless files

Delete useless files and create .gitignore for them
Add Observer pattern protocols

Add Observer and Observable protocols.
Add Singleton data storage

Added Singleton class, DataController, that contains all Departments.
Add initWithName:Birthday

Added initialization methods for Human (used to be in Student).
Fix issue with mutable public property, add Observer

Fixed an issue with mutable properties, implemented Observer pattern for calculation of average mark.
Implement HeadOfDepartment category

Implement HeadOfDepartment category of Teacher class. Can have subordinate teachers.
Implement Department.

Implemented Department, which has Head (Teacher) and Groups.
Changed average mark protocol

Changed average mark protocol, to be more concise.
Create sample hierarchy

Created sample hierarchy of objects with average marks, to test marsk counting.
Merge branch 'master' of https://github.com/alaershov/university-ios-assignment-1-2
Merge READMEm changed on github, with the rest of the project.