* Defnied more APIendpoints for feedback and subscriptions
 * Added the feedback spec to the docs folder
 * The previous commit also closes #43 and #68

* The mechanism remains partially incomplete as the progress in
  !67-create-new-model-feedbackline-and-integrate-it is blocking
  progress. Several tests for the API endpoint need to be written
  including. More validation and constraints might have to be added.
* This code was written with the assumption that the user model
  will hold group information in the future.

* on creation or deletation of an assignment of the subscription
  a new submission is looked up. Therefore, currently deleting an
  assignment may leads to SubscriptionEnded exception.
* Cleaned up the urls config

* The mechanism proposed should work as follows:
  * Tutors can subscribe to certain submission categries (currently
    this includes exam, student or type specific submissions).
    If the set of submissions to corrent is small (student) all
    submissions of that category are reserved for that tutor.
  * A reviewer should also be able to subscribe other users (delegation)
  * A subscription contains assignments or creates them:
    * Only one assignment per user may be active.
    * No new assignments can be added to a subscription after it was
      created while another assignment is present for that subscription.
    * An assignment delegates a submission to a tutor.
    * An active assignment indicates that the tutor is working on that
      assignment
    * After an assignment was finished it is deleted (or archived).
* Upgraded to Django 2.0

* Closes #66, #53.

This is needed for correct routing in the frontend

* no url configuration needed simply register viewset with router
* now using DefaultRouter, meaning api root is now browsable
* merged some views
* makes it easier to include api schema later
* Ran isort and updated docstring

* Also added docstrings to classes and module in views.py
* Removed a logging statement from StudentApiView

* ran isort on all test files

The methods in core.tests.data_factories.py are not finished nor good and overlap with GradyUserFactory.

Backend
- Added isStudent permission
- Added serializers apropriate for StudentPage
- Added api-endpoint urls
- Added views regarding StudentPage
- Migrated the Django Session Authentication to djangorestframework-jwt authentication

Frontend
- Migrated from vue-resource to axios because of better documentation & features
- Added Login Component
- Added First Part of StudentPage containing overview of exam and subissions

Closes #41
References #39

to User model

- It is now possible to run tests in the frontend.
- The backend authentication uses AbstractUser instead of
AbsstractBaseuser

- ran isort to properly sort imports
- reformatter some classes

Backend
- Added isStudent permission
- Added serializers apropriate for StudentPage
- Added api-endpoint urls
- Added views regarding StudentPage
- Migrated the Django Session Authentication to djangorestframework-jwt authentication

Frontend
- Migrated from vue-resource to axios because of better documentation & features
- Added Login Component
- Added First Part of StudentPage containing overview of exam and subissions

Closes #41
References #39

The project has been refactored so far as the current state of master has been placed under backend/ .
Some changes to the .gitignore and Makefile have been made to accomodate this refactor.