Entities created via an added component doesn't show up in scene graph

[vincentfretin]

Discussed in #754 (comment)
Suggested solution:
in SceneGraph.js, instead of listening to entitycreated, entityclone, listen to child-attached, child-detached, put back a debounce of 0 for rebuildEntityOptions and execute only if element will be shown in scene graph. So extract the filtering logic currently in rebuildEntityOptions into a includeInSceneGraph function that we can reuse just to check one element before calling rebuildEntityOptions