Aliiases in SchemaDict for renamed tags/attributes

[janssenhenning]

One thing that the schema dictionaries cannot handle period is renaming of tags and attributes. It might be nice if there would be an aliasing mechanism, where in one central place thes renamings are collected and the schema dictionaries could understand the old and new names and return the correct paths. It should be possible to swicth these off.

However, one downside of this would be that the code using aliases could be potentially more confusing.