FedVAE: possibly re-initialize classifier each global round

[emiliolr]

Currently, the classifier is consistently trained over all global epochs. However, our pipeline schematic indicates that it should only be trained after all communication is done. Add the ability to re-initialize the server classifier's weights each round (essentially training from scratch each round) to see if this makes a difference at all.

• Motivation: initial samples from the aggregated decoder may not be very high quality, which could direct classifier's weights towards a bad part of loss space.