Added support for "meshTransform" data entry for RenderObjects.

meshTransform can be provided through the Xflow data connected to RenderObjects.
The float4x4 value will me multiplied with the WorldMatrix to further transform the mesh.

As this is renderer independent, this functionality is entirely implemented inside of the RenderObject.
Several changes with respect to transformations

- Moved TransformAdapter from XML3D.webgl to XML3D.data
- Made <mesh> and <multimesh> transformable
- Move transformation handling from group adapter to Transformable
- Also moved shader handling to Transformable
- Added TransformFetcher as an abstract way to access transformations
- Added support to transform SubData