Implemented database blenddata module for JSON sources.

It retains most of the structure of the database blender
module.

Differences between blender and blenddata modules:

* Overall, much simpler interface.
* Removed of BlendFileData, BKE_Main, BlenderStruct, ListBase,
  ID.
* BlendData is analgous to BKE_Main and similarly
  ListBase -> Block.
* Primary changes are in the initialization functions.

The current database blender module is now deprecated and
will be removed in the near future.