activedisplay: add date/time settings

credit to 0xD34D for this addition and the original feature,
to PD for copy+pasting and introducing errors, and to
nuclearmistake and his janitorially artisanal contributions

ps3: remove an un-closed preference category with a missing title string... phail
ps4: move checkbox handling code to the CORRECT FUNCTION

Change-Id: Id7daa6bc8d1447f0d99fc09dc7c164112b464afd