move build related files from root of /utils to /utils/build subdirectory

This PR corresponds to the proposal made here: #3019

This PR does conflict with the move to a pure JavaScript-based build system.  If both PR's are desired I can update them so that they don't conflict.

Slightly off topic: At some point it may be useful to remove the relative paths from the include *.json files and instead have the base path of the /src directory given as an additional command line argument to build.js/build.py.