Neuron name service: expect array of skeleton IDs for unregistering
Neuron navigator: register with neuron name service to get annotation updates

Every node within the neuron navigatorthat deals with single neurons (neuron
node and active neuron node) lets the navigator register with the neuron name
service for its neuron. If such a node is removed, it is also runregistered.

Closes #782.
Neuron navigator: refresh active neuron before active neuron content is redrawn
Neuron navigator: handle de-selection of a neuron

So far the neuron navigator didn't handle if a neuron was deselected. With this
commit, the navigator will also remove highlightings if a selection is removed.
The active neuron node also updates itself to show no information anymore, if
a selection gets removed.
Merge branch 'navigator-annotation-updates'