Core/VMAPs: Fix object orientation

Merge https://github.com/249CAAFE40/mangos-wotlk/commit/2f8b8e55d99122d34be2a08cbdbd2d2b1ae172d1
Quoting original commit log:
This patch fixes 2 issues with the vmap extractor. 1) Incorrectly converts vertex coordinates. 2) Forgets to convert coordinates on triangle indices.

The effects of [1] causes models to be flipped. This isn't very noticeable on most trees as flipping a cylinder results in the same cylinder, but it's very noticeable on any non-symmetrical geometry (which, even includes trees, it's just harder to notice). [2] Didn't seem to be a problem when the coordinates were incorrectly converted, but when applying the correct conversion caused some triangles to be flipped (i.e. facing inwards).

You will need to re-extract vmaps and re-generate mmaps for these changes to take effect.

Fixes #417