message: Only insert HTML into the composer in RTE mode
  If MD mode is enabled, paste the plaintext equivalent.
diff: @@ -488,8 +488,7 @@ export default class MessageComposerInput extends React.Component {
  const currentContent = this.state.editorState.getCurrentContent();
  let contentState = null;
  -
  - if (html) {
  + if (html && this.state.isRichtextEnabled) {
  contentState = Modifier.replaceWithFragment(
  currentContent,
  currentSelection,
  