Sonar Minor Warnings: Magic numbers

Magic Numbers have been removed from the below classes 
* AbstractTextViewerStage, 
* AttributeSuggestionWalker, 
* ConfigStage, 
* Dialogs, 
* FileChooserList, 
* NothingMountedStage, 
* SandboxStage, 
* StringUtil, 
* TopListStage,