Added h5p url to player controller and enginecore method to request it

[clpetersonucf]

Adds the H5P URL to the list of parameters passed to the Materia engine core via the initWidget postMessage

Enables the Materia.Engine.getH5PUrl() method to be callable from H5P widgets

Paired with ljoks/Materia#3

The base branch was changed.

[FrenjaminBanklin]

Assuming there’s a corresponding change in Materia to write H5P_URL into the global scope, and assuming anything relying on the cores' getH5PUrl functions is okay with them returning undefined, this looks okay to me.

The only nits I would pick: if the creator controller is no longer checking for .swf widgets, the player controller probably shouldn't be checking for them any more, either. And the suggested change to the creator controller, but that's not really necessary.

[FrenjaminBanklin]

This works in two lines but it's a little harder to read. More verbosity would make it clearer, but would also bloat it a little. Fine either way.

Suggested change

	if (inst_id != null) sendToCreator('initExistingWidget', [instance.name, instance.widget, keepQSet.data, keepQSet.version, BASE_URL, MEDIA_URL, H5P_URL])
	else sendToCreator('initNewWidget', [widget_info, BASE_URL, MEDIA_URL, H5P_URL])
	let creatorMethod = 'initNewWidget'
	let args = [BASE_URL, MEDIA_URL, H5P_URL]
	if (inst_id != null) {
	creatorMethod = 'initExistingWidget'
	args = [
	instance.name,
	instance.widget,
	keepQSet.data,
	keepQSet.version,
	...args
	]
	} else {
	args = [widget_info, ...args]
	}
	sendToCreator(creatorMethod, args)