Allow default and custom messages in derived classes from PyomoException

[michaelbynum]

Summary/Motivation:

The new direct interface to Gurobi attempts to pass a custom message to IncompatibleModelError here:

pyomo/pyomo/contrib/solver/solvers/gurobi_direct.py

Line 273 in 32591c1

raise IncompatibleModelError(

. However, that exception does not currently except custom messages. This PR enables custom messages.

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[mrmundt]

Per discussion today, we are just going to put this new functionality directly into PyomoException rather than making a new class for it. I'll work on that.