[commhistoryd] Use mce directly to turn the screen on when displaying a notification.

There is nothing to be gained by using qmsystem for this. In addition, we just
immediately request that the screen be turned on rather than checking if it is
on first: this avoids a blocking DBus call to mce.
Merge pull request #19 from rburchell/no-qmsystem

[commhistoryd] Use mce directly to turn the screen on when displaying a ...