Remove some refs to ScriptEditor
Copied source from ScriptEditor and related classes. Preping for initial
refactoring.
Cleanup: move editor navigation actions to own class.
Cleanup: BracketInserter classes, getSourceViewer_
Cleanup of minor methods, NatureID, UI toolkit, etc.
Cleanup: AdaptedSourceViewer
Cleanup: createSourceViewer
cleanup and reorder methods.
Cleanup: move actions code
Cleanup: SemanticHighlightingManager.
Cleanup: move GotoMatchingBracketAction code
Fix regression: handle doSetInput before source viewer is created.