merge: upstream fixes (mutt/default)

 * Change the compose menu fields to be dynamically padded.
 * Rename 'sign as' to 'Sign as'; makes compose menu more consistent.
 * Make GPGME key selection behavior the same as classic-PGP. (see #3950)
 * Force hard redraw after $sendmail instead of calling mutt_endwin. (closes #3952) (see #3948)
 * Enable all header fields in the compose menu to be translated.
 * Auto-pad translation for the GPGME key selection "verify key" headers.
 * Improve the L10N comment about Sign as.