Uses interagent meta-schema instead.

This is to reflect current state of Heroku production schema. This
commit also reorders the schema properties to make it more readable for
humans.
Adds stability and strictProperties properties.

This is also to reflect current state of Heroku production platform API
as well as to follow the HTTP API Design Guide. Additionally this
commit also reorders the properties to make more readable for humans.
Fixes identity property and adds readonly property.

This is also to sync with current state of Heroku's Platform API
as well as to make sure it follows the HTTP API Design Guide.
Merge pull request #187 from c4milo/sync-up-with-heroku-schema

Syncs up with Heroku's platform API schema and HTTP API Design Guide