Dynamic fields based on fields parameter
One ActivitySerializer instead of ActivityDetail + ActivityListSerializer
Manually creating paginator class so args, kwargs are passed
Removed get_serializer from ActivityList(ListAPIView) since it doesn't
use it anyway. (It uses get_pagination_serializer)
Added a test to check if fields are modified dynamically on ActivitySerializer
Moved DynamicSerializer to api.serializers
Added DynamicListAPIView
added generic.DynamicRetrieveAPIView
removed fields from actiity.views.ActivityDetail
Changed import
some style changes
Merge pull request #61 from vplme/activity-serializer

Generic functionality to use to use serializers and views with 'fields=' parameter