Navigator: fixed errors with retrieving the list of selected neurons.

Uses an unlinked NeuronListNode internally in the HomeNode and the AnnotationFilterNode.
Could use some refactoring.
Navigator: NeuronNode must use neuron_name and not name for the SkeletonModel.
Otherwise the name of the SkeletonModel generated for the ActiveNeuronNode
is "Active Neuron".
Navigator: added TODO, there should be no need to load twice the annotations
for the ActiveNeuronNode.
Navigator: Active Neuron now lists its annotations, although this fix
is potentially covering an error elsewhere.