Merge branch 'u/pgee/DM-1067'
DM-1015 Simplifies GaussianFlux algorithm by using slots to calculate centroid and shape.

Remove the config options fixed, centroid, shape, and shapeFlag
Remove code from GaussianFlux.cc which is required to support the non-fixed option
Code is now equivalent to the previous setting fixed=True, centroid=current centroid slot
shape=current shape slot, shapeFlag=flag of current shape slot.

Now that the shapeFlag can cause GaussianFlux to fail, modify unit tests accordingly
DM-461 adds a new Exception class, FatalAlgorithmError in meas base

This is a newly created exception which is know by meas_base to be "FATAL".
Which means that if it is thrown, the loops of measurements on exposures
will be terminated.  As per Jim, the NO_PSF flag has been removed from various
algorithms, and replaces with a throw of this new exception.

Some unit tests had to be altered to account for the change in behavior.
Remove check for noPsf flag from this test.