Add required properties field to rules schema

Added an extra field in the JSON schema for mapping rules,
that specifies which properites are required.

There is a specific remote rule that may only have a type key.
This ensures that no other keys are specified.

Change-Id: I80f0e5b4bdc275db2d6cd06a81968cef33423a4d
Merge "Add required properties field to rules schema"