Add enablers for proximity based LPM display states

Replaces https://github.com/nemomobile/mce/pull/157

Re-use legacy N9 low power display states for proximity based one
that lights up the display briefly when proximity sensor input matches
a) device is taken out of pocket / flipped front side up on table
b) hand hovers over device that is lying on table

Both legacy D-Bus method calls and freshly added signals are used to
tell ui side whether lpm states are active or not.

New datapipe display_state_next_pipe allows tracking of the next stable
display state - this is used to make sure tklock and lpm state data is
sent to lipstick before display powerup starts so that final ui state
is known when the first rendering after display power up happens.

The ambient light sensor is powered up in parallel with display - and
kept powered up in the lpm display states.

Leds that are active in display off, are active also during lpm states.