Rewrite particle applier remover demo to get rid of the hacky particle modifier creation code

[hang-yin]

[hang-yin]

Check this comment: #699 (comment)

[cgokmen]

In the example, load some kind of particle applier (e.g. salt shaker) and remove all the particle applier stuff from the dishtowel (it should stay a particle remover by default). Then first move the shaker to apply the salt, and then move the towel to remove it. Ask Eric for more details.