Issue #966: PatientData interface should have a get method that is not integer based.

So every controller uses `SimpleNamedData`... Which uses a List.

I don't like this, because it somehow assumes that `T` is a list of named pairs of `DT`. If that is an assumption that we're willing to make, why not make it explicit? Get rid of `T` and make `PatientData` extend `List<ImmutablePair<String, T>>` instead of `List<T>`. But I'm not yet sure this is a correct assumption.

Plus, I'm not sure `get(String)` makes sense in general. We'll want a controller for measurements, and that is a plain list without names.