[sleeptimer] get a quick sleeptimer-function for Power-keys, selectable ...

...over Setup Remote. Also add calls for keymap.xml for other keys.

Both examples for the keymap.xml:

	<map context="GlobalActions">
		<key id="KEY_TIMER" mapto="sleeptimer_standby" flags="m" />
		<key id="KEY_SLEEP" mapto="sleeptimer_deepstandby" flags="m" />
	</map>