added view to add, edit, remove courses, admin template changes

changes in admin template:
 - regarding user table
 - - - Changed Banned fields to Active
 - - - Changed Delete field to Change Status

 - regarding courses
 - - - Added link to add course
 - - - Added search field (doesn't work for now)
 - - - Added table with courses, fields are the following:
 - - - - - - Id
 - - - - - - Category
 - - - - - - Author
 - - - - - - Name
 - - - - - - Description
 - - - - - - Image
 - - - - - - Active
 - - - - - - Edit
 - - - - - - Change status
 - - - Added edit button, for course editing
 - - - Added change status button, doesn't work for now, it requeires
update in db-api

changes in __init__:
- added routes for new views

- added template for course editing
- overall fixes and improvements