added findParticles() to JS api
added Particles.getParticleProperties() to JS
add example
fix comment
handle preventing edits to non-existant particles
added new example of particle bird
Merge pull request #1694 from ZappoMan/dont_edit_bad_particles

New particles JS features
Merge branch 'master' of https://github.com/highfidelity/hifi into metavoxels
MetavoxelDataPointer -> MetavoxelData, grid spacing as power of 2.