Add a button to fire up a file chooser dialog to select the name
of the encrypted or signed file to write.
Add an option to generated armored ASCII output instead of the
default binary output.
Assign a title to the encrypt/sign dialog.
Use the gtk_dialog_run function to display the encrypt dialog.
This make things slightly easier as we no longer need to connect
callbacks to the `clicked` signal from the buttons or the
`destroy` signal from the dialog.
This is Yorkie, a task-oriented graphical frontend for GnuPG.