Enable load function of Magnolia resource

In a JavaScript model you can load other js files which define other JavaScript classes.
Currently it works like this:

load(__PATH__ + "/../js/utils.js");

The _PATH_ variable is evaluated by the system, it is the path of the script (which calls load) on the file system.

This is breaking the concept that a JS model can be any Magnolia resource (currently a Magnolia resource can be from the file system, from classpath or a file representation in a JCR node).

An improved version should support something like this:

 loadScript('/path/to/resource/in/our/resource/origin')

e.g.

 loadScript('/javascript-model-samples/templates/js/formProcessors/saveContact.js')