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