Reconcile DRP and ICS build systems for pfs_utils

pfs_utils is intended to hold routines and configuration which should or might be used by both the ICS and DRP worlds (fiber numbering, telescope coordinate transforms, etc).

To make that work, it does not depend on any external packages which pull in significant pieces of the LSST or ICS stacks.

In order to install cleanly for the DRP, a SConstruct file has been added in the root directory. This then requires both scons and sconsUtils. And sconsUtils pulls in all sorts of handy things.

I think that since this is only an installation time issue, we can live with requiring sconsUtils and family. Should be OK at Subaru, LAM, and JHU in any case.

Still, it would be nice if we figured out how to avoid the requirement. And if not, we should make pfsinstall handle this more cleanly.

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