Peter's review feedback
-  FileViewController now listens to EditorManager's currentlyViewedFileChange event instead DocumentManager's currentDocumntChange event. This removes the need  to update the EditorManager's currentlyViewedFile property when setting the current document, i.e. by using the FILE_OPEN command.DocumentManager gets smarter about sending currentDocumntChange events, i.e. it won't send its clear method is called and no document has been current.
- rename CurrentlyViewedFile to CurrentlyViewedPath
- remove obsolete exports
- remove         _$previousCustomViewer
- jquery prefixes
-  no dependency on ImageViewer in Editor Manaeger