Example scene for EC_ParticleSystem. Now to hunt a bug

this does not work in current Tundra, not in git head nor 2.4.1 release, but works in older versions (e.g. 2.4.0 and 2.2.0 releases).

With current the particle asset does not get loaded, no matter what tricks I've tried.

Is good to merge as an example when works.. either if some asset ref prob is found in the example, or the bug is fixed in Tundra core.