message: resolve finished promise when closing dialog by clicking background
  ... by calling the same close method as otherwise and not
  have a special path that just calls the onFinished callback.
  This will also not close all the dialogs anymore,
  but that sort of seems like the intented behaviour?
diff: @@ -47,7 +47,7 @@ class ModalManager {
  } */
  ];
  - this.closeAll = this.closeAll.bind(this);
  + this.onBackgroundClick = this.onBackgroundClick.bind(this);
  }
  hasDialogs() {
  @@ -124,6 +124,7 @@ class ModalManager {
  );
  modal.onFinished = props ? props.onFinished : null;
  modal.className = className;
  + modal.close = closeDialog;
  return {modal, closeDialog, onFinishedProm};
  }
  @@ -216,28 +217,16 @@ class ModalManager {
  };
  }
  - closeAll() {
  - const modalsToClose = this._modals.slice();
  - this._modals = [];
  -
  - if (this._priorityModal) {
  - modalsToClose.push(this._priorityModal);
  - this._priorityModal = null;
  - }
  -
  - if (this._staticModal && modalsToClose.length === 0) {
  - modalsToClose.push(this._staticModal);
  - this._staticModal = null;
  - }
  -
  - for (let i = 0; i < modalsToClose.length; i++) {
  - const m = modalsToClose[i];
  - if (m && m.onFinished) {
  - m.onFinished(false);
  + onBackgroundClick() {
  + const modal = this._getCurrentModal();
  + if (!modal) {
  + return;
  }
  + modal.close();
  }
  - this._reRender();
  + _getCurrentModal() {
  + return this._priorityModal ? this._priorityModal : (this._modals[0] || this._staticModal);
  }
  _reRender() {
  @@ -268,7 +257,7 @@ class ModalManager {
  <div className="mx_Dialog">
  { this._staticModal.elem }
  </div>
  - <div className="mx_Dialog_background mx_Dialog_staticBackground" onClick={this.closeAll}></div>
  + <div className="mx_Dialog_background mx_Dialog_staticBackground" onClick={this.onBackgroundClick}></div>
  </div>
  );
  @@ -278,8 +267,8 @@ class ModalManager {
  ReactDOM.unmountComponentAtNode(this.getOrCreateStaticContainer());
  }
  - const modal = this._priorityModal ? this._priorityModal : this._modals[0];
  - if (modal) {
  + const modal = this._getCurrentModal();
  + if (modal !== this._staticModal) {
  const classes = "mx_Dialog_wrapper "
  + (this._staticModal ? "mx_Dialog_wrapperWithStaticUnder " : '')
  + (modal.className ? modal.className : '');
  @@ -289,7 +278,7 @@ class ModalManager {
  <div className="mx_Dialog">
  {modal.elem}
  </div>
  - <div className="mx_Dialog_background" onClick={this.closeAll}></div>
  + <div className="mx_Dialog_background" onClick={this.onBackgroundClick}></div>
  </div>
  );
  