AppHandler APP_DESTROY_AFTER exists and so does "RESOURCE_FAILED_TO_LOAD"

[markhealey]

I can't recall why there are multiple things happening on errors like this (and in other places) but this should be cleaned up.

In container.js, both of these are fired when a script fails to load:

F2.Events.emit('RESOURCE_FAILED_TO_LOAD', evtData);
...
_appScriptLoadFailed(appConfigs[0], evtData.src);

If nothing else, the former should be added to the F2.Constants.Events object. Let's mark RESOURCE_FAILED_TO_LOAD for deprecation.

[markhealey]

@montlebalm you wanna grab this since you were just in #220? After thinking some more on it, we need to keep that RESOURCE_FAILED_TO_LOAD event around and definitely mark it for deprecation.

Surprisingly, the docs have no mention of this event being fired in the life cycle which also needs to be addressed.

[markhealey]

Also just noticed this new event APP_SCRIPTS_LOADED is not in Constants but is well-documented.

https://github.com/OpenF2/F2/blob/1.4-wip/docs/src/container-development.md#when-are-scripts-loaded

Let's add it to Constants, too.

[montlebalm]

@markhealey Sure I'll take this one.

[markhealey]

Closed #227 in #142 v1.4.0