Small updates enabling loading of more v0.8 models.

[Richardn2002]

Submitting my work during implementing meshgroups (so that I can load Grillo's model for testing), but are unrelated to meshgroups.

Include physics parameter mapping mode YX (functional) and parameter binding opacity (deserialization only).

A proper checklist of new features in 0.8 compared to 0.7 is needed after this and implemented orderly.

[Speykious]

Relates partially to #63 it seems