message: Make all open/save dialogs modal
  Previously native file dialogs were opened as non-modal.  This can be
  really confusing as you can alt-tab out of the dialog into the main
  window and even potentially open another dialog.  This is not how
  native apps tend to work.
  fixes
diff: @@ -258,10 +258,11 @@ export function dialogLoadWorkspace(
  setWorkspaceFilename: (fname: string) => void
  ) {
  const {dialog} = electron.remote
  + const window = electron.remote.getCurrentWindow();
  const filters = [
  {name: 'Petmate workspace', extensions: ['petmate']},
  ]
  - const filename = dialog.showOpenDialog({properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -278,10 +279,11 @@ export function dialogSaveAsWorkspace(
  setWorkspaceFilename: (fname: string) => void
  ) {
  const {dialog} = electron.remote
  + const window = electron.remote.getCurrentWindow();
  const filters = [
  {name: 'Petmate workspace file', extensions: ['petmate']},
  ]
  - const filename = dialog.showSaveDialog({properties: ['openFile'], filters})
  + const filename = dialog.showSaveDialog(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -291,10 +293,11 @@ export function dialogSaveAsWorkspace(
  export function dialogExportFile(fmt: FileFormat, framebufs: FramebufWithFont[], palette: Rgb[]) {
  const {dialog} = electron.remote
  + const window = electron.remote.getCurrentWindow();
  const filters = [
  {name: fmt.name, extensions: [fmt.ext]}
  ]
  - const filename = dialog.showSaveDialog({properties: ['openFile'], filters})
  + const filename = dialog.showSaveDialog(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -305,10 +308,11 @@ export function dialogExportFile(fmt: FileFormat, framebufs: FramebufWithFont[],
  // loadFile callback with the file contents.
  export function dialogReadFile(type: FileFormat, loadFile: (data: Buffer) => void) {
  const {dialog} = electron.remote
  + const window = electron.remote.getCurrentWindow();
  const filters = [
  { name: type.name, extensions: [type.ext] }
  ]
  - const filename = dialog.showOpenDialog({properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -324,10 +328,11 @@ export function dialogReadFile(type: FileFormat, loadFile: (data: Buffer) => voi
  // importFile API to accept file contents.
  export function dialogImportFile(type: FileFormat, importFile: (fbs: Framebuf[]) => void) {
  const {dialog} = electron.remote
  + const window = electron.remote.getCurrentWindow();
  const filters = [
  { name: type.name, extensions: [type.ext] }
  ]
  - const filename = dialog.showOpenDialog({properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  