Code Generator for Eclipse Code

Only filter the generation drop down list when appropriate (drop down is enabled and legal combination). This fixes #25

Removed the now unused MultipleArtifactRegistry

Remove the use of MultipleArtefactregistry

moved method getShellDisplay int subclasses

Improve the logging stack to provide more compatibility

Refactored CodegenPlugin to seperate the UI components and mov them into the ui plug-in

Resolved the problem of an error when adding the import from a reference implementation (#36)

Completed implementation of selecting the reference implementation from a drop down list (#20)

Added extension point definition and the corrisponding helper class for #22

Validate the page after removing a row. This concludes #22.