Use a module/path mapping for RequireJS overrides instead of just paths.

Instead of attempting to derive the module portion of a RequireJS
override strictly from the path to the JS file, we now use a dictionary
where the module name must be explicitly specified.  This allows us to
compensate for files which do not follow a naming scheme that is
compatible with RequireJS without having to normalize all files.  This
is extremely important when using third-party dependencies.