[Performance] Make the VAB and SPH use the same terrain as in-flight & space center.

[aaronfranke]

As many of you know, 0.21 changed the space center to use the same terrain/models as in-flight to reduce the time needed to load up flights. Unfortunately, the VAB and SPH still take long to load, and I presume this is because they don't use the same terrain as in-flight and the space center.

Simply put, I propose that, for 0.22, the VAB and SPH internal scenery exists within the flight scenery just as the space center now does in 0.21.