[Devel] reimplementing using visitor pattern

Changing to the visitor pattern will make it easier to implement a SAX
reader and writer
[Devel] still implementing new visitor pattern
[Devel] reimplementing using visitor pattern

Changing to the visitor pattern will make it easier to implement a SAX
reader and writer

This is a commit so that i don't loose my work. The code currently does
not compile
[Major] major rewrite, now implemented SAX and DOM methods.

SAX works, DOM does not yet work. Simpler implementation now by not
having to modify domain objects so they can be persisted.