Drain holes reference position was saved slightly above the mesh to avoid problem when the hole is placed on flat or nearly flat surface
The depth of the hole was internally bigger than what the user has set to compensato for it
However, this leads to problem with scaling and makes reprojection of the holes on the mesh complicated
This commit changes the reference point to the point on the mesh and the extra elevation is handled when rendering and drilling the hole.
The change is reflected in 3MF drain holes versioning so that old 3MFs are loaded correctly.
Reprojection on the mesh after reload from disk/fix through netfabb has been enabled.
Drain holes are not allowed to be placed on its own inner surface. This was recently (0e3ebb3)
done by forcing invalidation of the slaposDrillHoles, which also invalidates and therefore
hides the drilled mesh. However, that also hides the hollowed mesh and it is not possible
to place holes inside the cavity.
This change does not dump the drilled mesh, but checks that no raycast hit ends up in a hole.
