* Implement fetch request editing.
* Implement predicate editing.

* Complete implementation of fetched property editor.

* make data model compatible to Xcode .xcdatamodel so that one can exchange or write universal projects
  - .xcdatamodel it is a file bundle (simple directory)
  - has two files
    - elements
    - layout
  - both are keyed archives
  - Xcode translates the .xcdatamodel into a .mom (a third keyed archive format)
    which becomes part of the bundle resources
  - so our GSCoreData should be capable of reading .mom
  - and DataBuilder should be able to write/generate .mom

* fix GUI glitches