Proposal for decoupling serving and computing of measures

Currently, the abstract class `Measure` is a representation of a JAX-RS resource. In order to implement a concrete measure, one has to extend `Measure` by a new class `MyMeasure`and to override its `compute` method. Hence a concrete measure is a concrete resource.

In terms of modularity, it would be preferable to decouple the measure computation and its serving as a resource. My proposal is to restructure the implementation as follows:

```java
public interface Measure {
SortedMap compute([...]);
}

public class MeasureResource {
private Measure measure;

public MeasureResource(Measure m, [...]) { ... };

/* optionally */
SortedMap compute([...]) {
return measure.compute([...]);
}
}
```
A concrete measure `MyMeasure` would implement the interface `Measure` and would be bound via the constructor `MeasureResource` to a concrete resource. Optionally, the class `MeasureResource` could implement a method `compute` that just delegates the computation to the computation to the underlying measure.