Connectivity widget: use correct ID to track selection of target neurons

Before, a combination of widget ID and skeleton ID was used to track the
selection state of the target neurons. This imposed to problem, but it
is more consistent to use the skeleton ID only, just like it is done for
all the partner neurons.
Connectivity widget: update synced widgets on selection change of target neurons

This fixes #697.
Neuron name service: get neuron name from back-end, too

So far, the neuron name was taken from the skeleton model's base name
field. This, however, isn't guarantied to always have the correct
value (discussed in issue #696). Therefore, the back-end is asked to
include this information when the front-end asks for all labeling
information (if it is needed).
Annotation search: sort annotation list alphabetically

This makes it much easier to look through the annotations of search
results and it fixes #693.
Merge branch 'synapse-risk-new'
GroupGraph: refactored risk measurement.

Also interpreting 0 as MIN and 1 as MAX, in edge labels.