Edited user models

- deleted ParentTeacher
- made teacher inherrit from parent
- made parent <> student in stead of student  > parent
Edited user models some more
Working on user views
Wrote permalink wrapper
Added comment in freevle.__init__
Added two cms templates
Installed markdown extension and updated readme
Wrote cms models and updated views and tests

- Made Category
- Made Subcategory
- Made PageSection
- Made TextSection
- Made ImageSection