relicense with MIT and simplify/update all the copyright information

[garyjg]

I am planning to change the license for this code to MIT and update the copyright notices. The goal is to make it easier for other SCons users to use the code for their own build configurations. I've already confirmed that MIT is an acceptable license for UCAR open source.

I've just removed all the files which were copied from other projects and had their own licenses. The only exception is colorbuildmessages.py, but since that was copied from the scons contrib wiki way back when and still contains an attribution, I think it must be ok to include. It still works, but if no one uses it, then maybe it should just be removed.

If anyone has objections or suggestions, please note them in this issue.