renamed PopulationSelection to Selection
implemented new projection syntax (and moved some old CSA files into
_old_projection sub-directory)
reformatted some old catalog entries to partially match new syntax.
Added unit-test for Projections, including simple example (for which I
had to update fix the ports of the HH class and add a Response type)
debugging the projection syntax code
debugged new projection syntax, basic test now passes. Also implemented
ConnectionRule reader (writer not done yet)
changed element name of Selection from 'Set'
removed duplicate Selection class in population.py in favour of the one
in the containers.py
Manually merge branch 'tclose-projection_syntax' into master

Conflicts:
	lib9ml/python/nineml/user_layer/components/base.py