Modify mapper policy file

This commit modifies the mapper file.  It incorporates changes made by
Andy B on his fork as well as a few changes added by Jim C on his fork.
Updated camera definitions for DECam

I added the code, input files, and resulting camera registry
for the DECam.  You can load the camera by doing:
>>> from lsst.obs.decam import DecamMapper
>>> mapper = DecamMapper()
>>> mapper.camera

chipcenters.txt has the bounding boxes of the chips and a rotation in
the plane of the focal plane.
segmentfile.txt has the amp information.  This is trivial until we
can look at DECam raw data.
Resolving rebase conflict with obs_decam.table
Updating UPS tables to be consistent with obs_cfht.
Building the DecamParsetask
Adding ccd number (MEF layer) into registry
Merge branch 'acbecker1' of https://github.com/SimonKrughoff/obs_decam into acbecker1