Fix camera rotate and zoom

[hietalajulius]

https://user-images.githubusercontent.com/4254623/115144763-1e8ba800-a057-11eb-94e2-99e7d4cd39d2.mp4

• Changes the mesh coordinates to be right handed/same as in open3d (corresponding dev-workspace PR to follow)
• Improves camera controls (zoom + rotation, adding translation in a follow up PR to avoid clutter)
• Camera math is somewhat inspired from here but without the mViewIsUptodate convolution spaghetti :spaghetti:
• The test might be a bit rough (hard coded constant values), happy to get feedback on that
• I hope changing SceneModel's camera to be a std::shared_ptr makes sense, mostly wanted to first compute the mesh mean before initializing the camera.