Reimplement profiles views with Generic Views from DRF

[weynelucas]

The profile views are good candidates to reuse some common patterns with Generic Views from Django REST framework and make the code more DRY.

ProfileRetrieveAPIView looks like this:

class ProfileRetrieveAPIView(RetrieveAPIView):
    permission_classes = (AllowAny,)
    queryset = Profile.objects.select_related('user')
    renderer_classes = (ProfileJSONRenderer,)
    serializer_class = ProfileSerializer

    def retrieve(self, request, username, *args, **kwargs):
        # Try to retrieve the requested profile and throw an exception if the
        # profile could not be found.
        try:
            profile = self.queryset.get(user__username=username)
        except Profile.DoesNotExist:
            raise NotFound('A profile with this username does not exist.')

        serializer = self.serializer_class(profile, context={
            'request': request
        })

        return Response(serializer.data, status=status.HTTP_200_OK)

Using generic views features, will look like this:

class ProfileRetrieveAPIView(RetrieveAPIView):
    permission_classes = (AllowAny,)
    queryset = Profile.objects.select_related('user')
    renderer_classes = (ProfileJSONRenderer,)
    serializer_class = ProfileSerializer
    lookup_field = 'user__username'
    lookup_url_kwarg = 'username'