Make OrbitControls mouse buttons configurable

Update loader-assimp2json example

Update loader-assimp2json example: assimp.json is the new extension for assimp2json JSON files and a format metadata header is added to the format.

WebGLRenderer: Deallocate Object when removed from scene graph (no need for object.dispose()). See #5269.

BufferAttribute: Simplify cloning

Update to mrdoob/three.js#5262

Update to mrdoob/three.js#5262

Update Frustum.html

added minor improvement to docs. Also, the name of the Frustum's method should reflect the explanation and be changed to intersectsObjectBoundingSphere(...)

BufferGeometry: Clone attributes