Migration

##r49 => r50dev

• texture coordinates aren't anymore flipped in the geometries, instead textures have flipY property (true by default); unflipping not yet finished for all geometries; all models need to be re-exported / reconverted (tools have been updated as well)
• PlaneGeometry changed back to vertical orientation (facing screen instead of laying on the ground)
• doubleSided / flipSided properties moved from Object3D to Material
• objectMatrix in shaders was renamed to modelMatrix
• JIT caching removed from Animation

##r48 => r49

• changed PlaneGeometry from vertical to horizontal orientation
• renamed __dirtyXXX attribute properties to xxxNeedUpdate
• removed Vertex class, use Vector3 instead