Explicitly check for good soma in examples/morph_check.py
Explicitly check for good soma in examples/morph_check.py

Output with good data:

    Check file test_data/swc/Neuron.swc...
    Has valid soma? True
    Has axon? True
    Has apical dendrite? True
    Has basal dendrite? True
    All neurites have non-zero radius? True
    All segments have non-zero length? True
    All sections have non-zero length? True

Output with bad data:

    Check file test_data/swc/Single_apical_no_soma.swc...
    Has valid soma? False
    Cannot continue without a soma... Aborting

Change-Id: I5007dcde22a8f82cab3af86f8c569879d7aa6104

wizmer/NeuroM,lidakanari/NeuroM,mgeplf/NeuroM,BlueBrain/NeuroM,eleftherioszisis/NeuroM,liesbethvanherpe/NeuroM,juanchopanza/NeuroM