Add v1.0 Operator API

[oubiwann]

Official docs are here: http://mesos.apache.org/documentation/latest/operator-http-api/

Tasks:

• [ ] Implement Operator API protobuf types - ticket #33
• [ ] Implement Operator Calls - ticket #12
• [ ] Provide Default Handler for Operator Events - ticket #13

Part of epic #2

[wdhowe]

This Task can be marked as complete: Implement Operator API protobuf types - ticket #33