Update the model   - Add primary key to all models   - Go over the mandatory and optional relationship to make sure it works like it supposes to   - Add __str__() method for all models   - Add a blank option to a few of the field
Update the model
  - Add primary key to all models
  - Go over the mandatory and optional relationship to make sure it works like it supposes to
  - Add __str__() method for all models
  - Add a blank option to a few of the field

Resolving part of issue #4

khoa102/MyBlog,khoa102/MyBlog