New interfaces for json_schema + hardware_product associations

[karenetheridge]

These usecases should be supported:

• view validation results for a device (see also handle changes to validation result responses #299); click through to the JSON Schema that was used for that validation. should be able to identify the specific schema (and section) where the failure occurred.
• view what (active) JSON Schemas exist in the db
• view the definition of a JSON Schema
• create a new JSON Schema
• inform conch-api that a particular JSON Schema should be used for validating particular hardware (and also remove a json_schema+hardware_product association)
• allow editing an existing JSON Schema (and, optionally, then update all hardware that use that schema to use the new version)

(see joyent/conch-api#1084)