Fine-grained debug configs

Add ability to enable/disable various debugging aspects.

To begin with, we'll allow that for tracing calls on WebgL.

For example:

/* Set all debug settings in one shot:
*/
SceneJS.setDebugConfigs({
    webgl: {
        trace: true
    }
});


/* Set a particular debug setting:
*/
SceneJS.setDebugConfigs("webgl.trace", true);


/* Get all config settings:
*/
var cfg = SceneJS.getDebugConfigs();
alert("WebGL trace enabled: " + cfg.webgl && cfg.webgl.trace);


/* Get the WebGL settings:
*/
cfg = SceneJS.getDebugConfigs("webgl");
alert("WebGL trace enabled: " + cfg && cfg.trace);


/* Get the WebGL trace setting:
*/
var trace = SceneJS.getDebugConfigs("webgl.trace");
alert("WebGL trace enabled: " + (trace == true)); // Might be undefined

Also support: traversal logging using info text on Nodes.