Add 'menu' sub-command.

'cat' alternative that pops up a menu for selecting a file to print
(requires dmenu).
Further refactoring of some common sub-command arguments.

Basically just the two variants of -f/--force.
Add a pre-passphrase-entry anti-tty-print check.

Makes it less annoying when you forget '-f'.
Add -X/--gui mode.

Uses ssh-askpass/zenity/[g]xmessage for getting passphrase and
displaying status messages.  Combines nicely with 'menu'.