update serializer fields to include all relevant model fields
- update api/v1/image response to include:
- name
- platform
- url
- update api/v1/event response to include:
- instance_id
- machineimage_id
- url
- update api/v1/instance response to include:
- account_id
- update tests to assert that these things (among others that we weren't previously checking!) are actually present in the responses