CMB with OCE.

Get SMTK (and thus ModelBuilder) built with CGM support enabled.

Also, on Mac OS, this eliminates the Apple-specific build instructions; they weren't that different, were getting out of sync, and are really !*&%)@# hard to debug when you don't know they exist. That leaves the shiboken library possibly-improperly-installed on OS X, so please review with that in mind.