Support loading of mixing

See https://github.com/strongloop/loopback-datasource-juggler/pull/201
Implement mixin loading

In accordance with the latest mixin cleanup in juggler.
Support loading of mixing

See https://github.com/strongloop/loopback-datasource-juggler/pull/201
Implement mixin loading

In accordance with the latest mixin cleanup in juggler.
Removed normalization (see: juggler)
Fix conflicts
Fixed