Add never-blank-display mode

Debugging feature that allows blocking of display state transitions
so that the display is never blanked.

Control via mcetool --set-never-blank=enabled/disabled.

The setting persists over mce restarts and device reboots.

[mce] Support for never-blank-display mode added
Rename mcetool option --set-tklock-noblank to --set-tklock-blank

The negative part of the long option name does not make any sense.
Setting demo-mode also disables/enables blanking from lock screen

That is
"mcetool -Don"  implies --set-tklock-blank=disabled
"mcetool -Doff" implies --set-tklock-blank=enabled

[mce] Setting demo-mode also disables/enables blanking from lock screen
Merge pull request #57 from spiiroin/demo_mode

Setting demo-mode also disables/enables blanking from lock screen
Merge pull request #58 from spiiroin/neverblank

Add never-blank-display mode
Bump mce version to 1.12.16
Delay display state signal broadcasting after suspend

When making transition from display=off, mce waits for frame buffer
resume to finish before sending the display state change signal.

[mce] Delay display state signal broadcasting after suspend
Document the reason for using a worker thread to wait for frame buffer wakeup
Merge pull request #59 from spiiroin/delayed_display_status_ind

Delay display state signal broadcasting after suspend
Bump mce version to 1.12.17