UNITSOFMEASUREMENT-68: Remove DimensionService 

Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-68
UNITSOFMEASUREMENT-69: Rethink hierarchy (and possibly naming) of
Quantity and Measurement 
Probing how context specific multiply() could work
Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-69