initial nrn GHK exporting + tests
self contained ghk test files
organizing
generation of .mod files for GHK formalism. Requires changes to the NeuroML2 Schema, to be merged into org.neuroml.model
removed provisional GHK test, added GHK test to full NeuronWriter test
removed provisional GHK test, added GHK test to full NeuronWriter test
Merge branch 'ghk' of github.com:NeuroML/org.neuroml.export into ghk
Merge branch 'development' into ghk

Conflicts:
	src/main/java/org/neuroml/export/neuron/NeuronWriter.java
Merge pull request #12 from NeuroML/ghk

Major restructuring in NeuronWriter