SMM — Add defaultQuery to Measure

The Measure class lacked a way to provide a default value when some children measure has no measurands. The defaultQuery plays that role.

Discussion:
The defaultQuery is simply a small improvement to handle the specific case where a non-direct measure (i.e. a measure that depends on another for its value) happens not to have any available value from what should have been its "base measure". This allows us to specify a default query or value to be returned instead of either null or of failing the measurement. This is a normal situation that can happen when certain optional "children" don't exist.

Summary of change:
· Add named relation default [0..1] form Measure to Operation

• Add named relation defaultQuery [0..1] from Measure to Operation