- fix wrong cast to Spatial in AssetDataObject
- cleanup and unify opening/closing of AssetData objects
- add logging for opening/closing of AssetData
- close associated assets when closing models (e.g. textures, materials etc.)
git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@10310 75d07b2b-3a1a-0410-a2c5-0572b91ccdca