MultiTargetTracker __next__ fails for MultipleHypothesis associations

[ztarsasw]

v 1.1
MultiTargetTracker
ExtendedKalmanUpdater
PDAHypothesiser
PDA Data Associator

When running a MultiTargetTracker with a data associator that returns a MultipleHypothesis object from it's associate method, the next method of MultiTargetTracker fails as the Updater expects a Hypothesis type that contains a prediction attribute. My guess is that the check for hypothesis on line 220 in stonesoup/tracker/simple.py needs to be extended to handle the MultiHypothesis case.

Definitely possible I have an implementation issue, but this seems more like a case that should be supported by the MultiTargetTracker type.

[ztarsasw]

Just as a follow up, when I changed my implementation to use a MultiTargetMixtureTracker, things worked as expected. This might be intended behavior, but recommend clarifying this in naming/docs if so. As a user, it's not clear that "Mixture" = "Supports MHT" without reading the source code, though that term may be defined elsewhere in the docs.