Add init and configure event to AppBase

[lucaheft]

Description

Adds 2 new generic events to AppBase

init -> Fired after AppBase.init
configure -> Fired after successfull AppBase.configure

I've noticed, that there are no jsdocs for events in AppBase, if desired I can add those as well

If this gets merged we also want to reflect these changes on the developer site Application Lifecycle

Checklist

• I have read the contributing guidelines
• My code follows the project's coding standards
• This PR focuses on a single change

[mvaligursky]

How strange the events are not documented. I'll put on my list to document.

Please document yours though - see how these are done:

engine/src/scene/scene.js

Lines 32 to 81 in 25effe0

	class Scene extends EventHandler {
	/**
	* Fired when the layer composition is set. Use this event to add callbacks or advanced
	* properties to your layers. The handler is passed the old and the new
	* {@link LayerComposition}.
	*
	* @event
	* @example
	* app.scene.on('set:layers', (oldComp, newComp) => {
	* const list = newComp.layerList;
	* for (let i = 0; i < list.length; i++) {
	* const layer = list[i];
	* switch (layer.name) {
	* case 'MyLayer':
	* layer.onEnable = myOnEnableFunction;
	* layer.onDisable = myOnDisableFunction;
	* break;
	* case 'MyOtherLayer':
	* layer.clearColorBuffer = true;
	* break;
	* }
	* }
	* });
	*/
	static EVENT_SETLAYERS = 'set:layers';
	/**
	* Fired when the skybox is set. The handler is passed the {@link Texture} that is the
	* previously used skybox cubemap texture. The new skybox cubemap texture is in the
	* {@link Scene#skybox} property.
	*
	* @event
	* @example
	* app.scene.on('set:skybox', (oldSkybox) => {
	* console.log(`Skybox changed from ${oldSkybox.name} to ${app.scene.skybox.name}`);
	* });
	*/
	static EVENT_SETSKYBOX = 'set:skybox';
	/**
	* Fired before the camera renders the scene. The handler is passed the {@link CameraComponent}
	* that will render the scene.
	*
	* @event
	* @example
	* app.scene.on('prerender', (camera) => {
	* console.log(`Camera ${camera.entity.name} will render the scene`);
	* });
	*/
	static EVENT_PRERENDER = 'prerender';

[Maksims]

configure - seems generic in this context. Like application is configured, but with what and by whom?
Really it is something like: config:loaded because this is very specific to way Editor outputs the project and provides config.json with data in it. Engine only users usually don't use that approach. A bit more info in description of the event - will be useful.

[lucaheft]

I see, not sure how to go forward with this. How about we only add init event for now?

[Maksims]

I see, not sure how to go forward with this. How about we only add init event for now?

I think if you name second event as config:loaded - should be fine.

[lucaheft]

I just tried this out and it seems like when launching in the editor (use_local_engine), these events are not called. However when downloading they work correctly.

I guess there is some custom editor startup which doesn't call init and configure of the AppBase?
This could be quite confusing for the user.
Can this be changed in the editor, so the behaviour is similiar to the exported editor project?

In my test I subscribed to the events in the loadingscreen