Add enablers for evdev event mapping

MCE assumes that certain events have strongly defined meaning, but on
some devices kernel is emitting events that do not match expectations
that mce has about them.

Make it possible to add configuration files that are used to translate
events kernel is emitting into what makes logical sense to mce.

[mce] Add enablers for evdev event mapping
Make keypad slide policies work again

During tklock rewrite display blanking and autorelock policies based
on keypad slider state were broken.

Make keypad slide out/in work similarly as it used to with Nokia
N900 and N950 devices: Unblank display and hide lock screen when
keypad is slid out. If display was turned on due to keypad slide and
no touch input / calls are observed, blank display when the keypad
is slid in again.

[mce] Make keypad slide policies work again. Fixes JB#24391
Merge pull request #227 from spiiroin/jb24391_keypad_slide_policy

Make keypad slide policies work again
Bump mce version to 1.38.0
WIP restart sensord when both volume keys and power button are pressed

LED blinks:
1) green when both vol keys are down
2) yellow when power button is pressed too
3) red when keys are released -> sensord restart is initiated

The red blinking is stopped 3 seconds after reply to dbus method
call from systemd is received.