Don't automatically sort params to left of export.

The intent was to put properties that are per-run "inputs" to the model to the left of properties that are per-run "outputs" of the model. But there are legitimate cases for putting builtin properties in the exports, and this mechanism can't decide where to put them. Moreover authors should be able to rely on the order being what they requested, and are perfectly capable of choosing a sensible order.
sensor model: unitless properties should have labels

The logging system requires that each per-run property have a PropertyDescription with a label attribute. However sensorType doesn't have units, so we were not previously assigning a PropertyDescription to it.

Eventually, the "unit type" notion should be extended to handle categorical properties.

Possibly worth putting into LabModelerMixin too.

IS [#48363865]