Added getJobSummary API so it can be used by the role and role/environment page in the UI.

Refactored code from SchedulerzRole and SchedulerzRoleTest into relevant classes so it can
be used by the UI and the thrift API.
Added tests for new code.
Moved populateJobConfig call into ReadOnlyScheduler.

Testing Done:
gradle clean build
gradle run to test local UI.

Bugs closed: AURORA-64

Reviewed at https://reviews.apache.org/r/17303/