Progmesh Simplification for Matterport3D Scenes

[Skylion007]

🚀 Feature

Semantic Mesh Simplification for MP3D.

Motivation

Initial Testing shows that simplifying the MP3D semantic meshes with #468 shows significant speeds ups. However, the feature is not stable and segfaults on certain scenes. I am opening this issue to resolve those and see if this functionality can be merged into the HabitatSim.

Pitch

Initial tests show a 50%+ increase in the speed of RGBD+Semantic Sensor on some MP3D scenes.

Alternatives

Use another mesh library. It's probably too slow to do on the fly, but we should have scripts to convert the scenes.