Basic schema validation added to images calls.

* register/tag/untag are now covered by json schemas

Partailly implements blueprint savanna-rest-api-1-0-validation

Change-Id: I407b0f34e8fd954a2911e550856aeb42101cac65
Placeholders for future validators and schemas

Change-Id: Ib8cf11d47ca5959cd1784559a9e7d096e0c4fbb0
Merge "Basic schema validation added to images calls."
Merge "Placeholders for future validators and schemas"