added POST/GET for video

@ormsbee 
When you organize your imports, please group in the following order:
1. stdlib includes
2. 3rd party includes
3. local code includes

So in this case:

```python
from django.http import Http404
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status

from edxval.models import Video
from edxval.serializers import VideoSerializer
```