Renamed Quota to ResourceAggregate.

Updated client to use the new struct.

Testing Done:
Successfully ran:
gradle clean build  && ./pants src/test/python/apache/aurora/client:all
On a local scheduler tested /scheduler* and /quotas end points.

Will run end to end test tonight.

Bugs closed: AURORA-105

Reviewed at https://reviews.apache.org/r/18546/