Split requirements.txt

This splits requirements.txt three ways: preinstall_requirements, which
contains packages imported by other packages' setup.py,
test_requirements, which is for stuff only useful to devs, and
requirements.txt, which is just our dependencies

	new file:   preinstall_requirements.txt
	modified:   requirements.txt
	new file:   test_requirements.txt
Install scripts under ./scripts to $PREFIX/bin

This means we can just run 'run_pipeline.py' anywhere as long as the
virtualenv is active.
	modified:   setup.py