Remove Asset object
After updating to DotAAS version 3.0-rc1, we can remove the Asset object from our model, since it does not provide any information anymore.
To do so, we should:
- remove class
Asset
- drop Assets in deserialized files silently
- still, add an empty
Assets
list to serlized files to stay compliant to the schemas - remove KeyElements.ASSET
- change Keys with type==Asset to type==GlobalReference in deserialized files silently
- Mention how we handled assets in (module) docstring(s)