This PR aims to fix the wrong unit scaling issue with FBX models.

Currently, in projects made with Overload, we tend to counter-scale our objects with a 0.01 scale to compensate the centimeters to meters conversion.

The idea here is to add a flag to automatically convert these FBX using centimeters as the default unit to meters (In order to avoid manual counter-scaling).

Do note that this PR will break scenes made with previous version of Overload. If you want to convert your scene to correctly behave with this new scaling system, you'll have to disable GLOBAL_SCALE in your model asset properties.

This PR introduce several flags for models:

• GLOBAL_SCALE (On by default, disable it if you want your scenes created with older version to remain unchanged)
• EMBED_TEXTURES
• FORCE_GEN_NORMALS
• DROP_NORMALS
• GEN_BOUNDING_BOXES (No actual usage, as we do not care about assimp generated bounding boxes)

TODO:

• Update Assimp to 5.0.1
• Add Assimp 5.0.1 new flags to EModelParserFlags
• Update engine models (Cube, Cone, Plane...)
• Update editor models (Gizmo arrows, Camera...)

Fixes #136