implementing assortativity (wip)
calculate assortativity coefficient and return single value
Assortativity.properties + writeData
debugged calculation of the assortativity coefficient
complete implementation: Assortativity coefficient (Newman, 2002, Assortative Mixing in Networks)
Merge branch 'feature/metric_assortativity' into develop

Conflicts:
	src/gtna/Exploring.java