Added select compound node to compiler:

- Added indentation to DIS compounds for readability
- Added the ability to modify DIS object strings after creation to allow more flexible ordering
- Made the graphconverter more general
- Added conversion functions for selectCNode
- DIS object now keeps track of the node -> key mapping
- node -> key mapping is done separately for to and from relations
- Various changes to graphconverter for compound nodes
- Some examples changed for testing and from compiler changes