Avoid nonsense crash when player asks crew to dock at a planet
Added the ModManager support to the new ModelViewer.
Makes it easier to develop new mods with models.
Convert & remix Natrix for SGModel.
Print more log messages in modelviewer, fill UV coordinates with 0 if they don't exist

Closes #1952, closes #1876
Scaling & landing gear positioning helper model
Toggle scale/landingpad test with p.

Closes #1981.

Gun/pad resources are cleared with the model because texture cache clearing would remove their textures as well.
Merge remote-tracking branch 'luomu/modelviewer-tweaks'
Merge remote-tracking branch 'fluffyfreak/ModSupportModelViewer'
Merge remote-tracking branch 'luomu/sgnatrix'
Merge remote-tracking branch 'brianetta/Kroo'