Build Script

Adds a python based build script and documentation.  The build script assumes that regions are now to be hosted in their own repos with a structure described in the readme.  Non-Core plugins have started to be migrated to their own repositories.

The https://github.com/CoastalResilienceNetwork/gulf-of-mexico-region region has been modified to support building by this build script.
Does the script abort if a bad sha1 is used?