message: Fix up support for mimetypes and highlighting in the TextAceViewer.
diff: @@ -33,7 +33,7 @@ import * as ViewerElementTypes from '../viewers/ViewerElementTypes';
  import {emitResizeEvent as VirtualScrollAreaEmitResizeEvent, SetterState, VirtualScrollable} from '../VirtualScrollArea';
  import { ExtratermAceEditor, TerminalRenderer } from "extraterm-ace-terminal-renderer";
  -import { Command, DefaultCommands, Document, Editor, EditSession, MultiSelectCommands, Renderer, Position, UndoManager } from "ace-ts";
  +import { Command, DefaultCommands, Document, Editor, EditSession, MultiSelectCommands, ModeList, Renderer, Position, UndoManager } from "ace-ts";
  const VisualState = ViewerElementTypes.VisualState;
  type VisualState = ViewerElementTypes.VisualState;
  @@ -157,6 +157,7 @@ export class TextViewer extends ViewerElement implements Commandable, AcceptsKey
  this._aceEditSession = new EditSession(new Document(""));
  this._aceEditSession.setUndoManager(new UndoManager());
  + this._aceEditSession.setUseWorker(false);
  const aceRenderer = new TerminalRenderer(containerDiv);
  aceRenderer.setShowGutter(false);
  @@ -325,15 +326,12 @@ export class TextViewer extends ViewerElement implements Commandable, AcceptsKey
  setMimeType(mimeType: string): void {
  this._mimeType = mimeType;
  - // const modeInfo = CodeMirror.findModeByMIME(mimeType);
  - // if (modeInfo != null) {
  - // if (modeInfo.mode !== null && modeInfo.mode !== "null") {
  - // LoadCodeMirrorMode(modeInfo.mode);
  - // }
  - // if (this._codeMirror !== null) {
  - // this._codeMirror.setOption("mode", mimeType);
  - // }
  - // }
  + const mode = ModeList.getModeByMimeType(mimeType);
  + if (mode != null) {
  + this._aceEditSession.setLanguageMode(mode, (err: any) => {
  + this._log.warn(err);
  + });
  + }
  }
  getMimeType(): string {
  @@ -528,10 +526,8 @@ export class TextViewer extends ViewerElement implements Commandable, AcceptsKey
  // From viewerelementtypes.SupportsMimeTypes
  static supportsMimeType(mimeType): boolean {
  -// FIXME
  - return mimeType === "text/plain";
  - // const mode = CodeMirror.findModeByMIME(mimeType);
  - // return mode !== null && mode !== undefined;
  + const mode = ModeList.getModeByMimeType(mimeType);
  + return mode !== null && mode !== undefined;
  }
  deleteTopLines(topLines: number): void {
  