IntensityThresholdInstanceMaskSegmentationModel enforces a mono image but itself is not initiated with a channel

Simplified RoiSetWithDerivedChannels, now simply appends all derived channels in series.  Test confirms that multichannel derived accessor is used.

Instantiate models with keyword arguments now, no longer via "params" dictionary; although API still uses this name when passing Pydantic parameters models.  API describes model via its info property now, which passes instance property, not its init arguments.

Renamed some model classes; expanded scope of trivial object classification model to be functional base on intensity threshold, too