Add LOD models for the monsters to boost performance with lots of monsters in the map and fix some LOD related bugs

I've generated some basic LOD models for the new monsters added in 0.8.5 to help with the performance drops from having a lot of monsters around.
From the sources these were made with Blender by using the Decimate tool, _lod1 uses a Ratio of 0.25 and _lod2 uses a Ratio of 0.05.

Also included is a fix for a bug encountered during testing; LOD models were being recalculated when switching between them due to the code only checking if the model's index matches that of the initial LOD state.
LOD will now be calculated automatically on client-networked models (misc_clientmodel, func_clientwall) reducing the work needed for mappers to make use of their performance boost.