#174 add and view photo and audio to enquiry

Since most of the photos and audio infrastructure was already in place, we refactored lots of code to be reusable for both the enquiry and child media.
Changes include the following
- Introducing a base model for enquiry and child to prevent duplication of photos and audio 
- Refactored child_media controller to media_controller and made it generic to handle media for enquiry and model