Copying text field/attributes too when copying runnables

Needed for XPath like expressions:
select="speciesList[ion='ca']/concentration"
Merge branch 'master' into development

Conflicts:
	lems/sim/runnable.py
More work to test Ca dynamics cell
Quick temp fix for div by zero
More explicit catching of div by zero error
Improved xml export of Unit
Fixed running conditional variables

Improved loading of NeuroML based LEMS models
Adding support for more functions
Adding initial test for parser
Update to v0.3.1
Lots more debug info if debug flag set to True in individual classes...