Neuron name service: add basic name generation and client update

This commit extends the neuron name service to generate names for each
skeleton it manages. Currently, this is only the base name fallback and
no data is requested from the back-end, yet.
Neuron name service: add skeleton ID as display option
Neuron name service: add support for all and own annotation labeling
Selection table: let 'sort by name' use neuron name service
Neuron name service: support meta annotation based labeling
Graph widget: retrieve names from name service
Compartment graph plot: use name service for labeling
Connectivity widget: get neuron labels from name service
Connectivity widget: remember checkbox states on threshold change