message: Clean up the imports in ViewerElement a bit
diff: import * as fs from 'fs';
  import * as Util from './gui/Util';
  -import * as VirtualScrollArea from './VirtualScrollArea';
  +import * as CodeMirrorOperation from './CodeMirrorOperation';
  +import {VirtualScrollable, SetterState} from './VirtualScrollArea';
  import {Mode, VisualState, CursorMoveDetail} from './ViewerElementTypes';
  import {ThemeableElementBase} from './ThemeableElementBase';
  -import * as CodeMirrorOperation from './CodeMirrorOperation';
  -type VirtualScrollable = VirtualScrollArea.VirtualScrollable;
  -type SetterState = VirtualScrollArea.SetterState;
  export abstract class ViewerElement extends ThemeableElementBase implements VirtualScrollable {
  