Only pick when the model has pointer event listeners to hear it.
Test case for https://github.com/virtual-world-framework/vwf/pull/251.
Fix `does not have a valid behaviors array` warnings.

Prototypes with URIs not matching `RegExp( "^http://vwf.example.com/" )`
(including relative URIs) could appear ready before they were fully
constructed. References to the incomplete prototype would cause any
number of errors, including the `behaviors array` warning and different
sorts of references to `undefined`.

`kernel.createNode` allows lookups by node ID in addition to lookup by
descriptor, which the constructed node and its ID derive from, and by
URI, which the descriptor derives from.

`kernel.createNode` was not blocking out IDs of nodes that had begun
construction but had not yet completed. If a new node was created that
had a partically-constructed node as its prototype, and if the
prototype's URI matched its ID, then the new node would begin
constructing before the prototype was ready.

The solution is to not recognize a value as an ID if it would refer to a
node still being constructed.

See https://github.com/virtual-world-framework/vwf/pull/251.
Merge pull request #294 from virtual-world-framework/branch/mars-improvements

Branch/mars improvements
Merge pull request #295 from virtual-world-framework/mars-game-staging

Mars game staging
Changes the fs call to watchFile from watch so Cesium will load
Turn on pointer events if app adds a pointer event listener on the scene
Request pointer events if app adds any event listeners for touch events
Merge pull request #297 from virtual-world-framework/branch/pointer-events-on-scene

Branch/pointer events on scene
Merge pull request #296 from virtual-world-framework/branch/cesium-nodejs-fix

Changes the fs call to watchFile from watch so Cesium will load
Added method to graph groups to set child properties
Added property to set planes doublesided