Neuron dendrogram: make setter more robust

Imporove robustness of option setters by parsing set value with Boolean().
Neuron dendrogram: add blacklist option to tree creation
Neuron dendrogram: add option to collapse 'not a branch' nodes

A node will be skipped if it is tagged 'not a branch' and this option is
activated (which it is by default).

Closes #815