OBJExporter: handle children objects

+ scale factor param
loaders documentation: xhrloader, objloader, mtlloader
Cache, LoadingManager, OBJLoader, ObjectLoader, TextureLoader and XHRLoader documentation
add BabylonLoader documentation
Merge remote-tracking branch 'upstream/dev' into doc.loaders
OBJExporter: convert indents (spaces to tabs)
Handling case when the orientation of VR state is null. For some devices the information might not be available and the API will return null
Merge pull request #5478 from dmarcos/nullOrientation

Handling case when the orientation of VR state is null. For some devices...
Merge remote-tracking branch 'upstream/dev' into doc.loaders
working on loaders docs, with new cross doc syntax
missing LoadingManager in some loaders
Simplified VRControls.
VRControls: Fixed typo caught by @WestLangley in ef93c0d287c132107a95a05ea4a496938a3be7ba.
working on loaders docs, with new cross doc syntax
navigator.mozGetVRDevices check is not necessary anymore since Firefox dropped the prefix
Merge pull request #5484 from dmarcos/dropsMozPrefix

navigator.mozGetVRDevices check is not necessary anymore since Firefox d...
grammar errors
Simplified ExtrudeGeometry UV code.
Updated builds.
Adds method to zero VR sensors