Major version condition overhaul for Bethesda NIFs

Also some decoding and major corrections.

NiParticlesData and NiPSysData were almost completely wrong.  NiGeometryData was wrong.  NiGeometry was wrong.  This was mostly due to Bethesda changing or breaking inheritance for derived types.

For Bethesda 20.2 NIFs NiParticlesData now inherits from NiObject directly.  NiParticleSystem changes between BSGeometry or NiGeometry based on version.

This resulted in NiPSysData and NiParticleSystem being almost completely wrong for later Bethesda versions.

Also changed all misuses of `User Version` to differentiate Bethesda versions to `User Version 2`.