hidpi: Make many places Hi-DPI aware.

This also introduces a getter for the mnDPIScaleFactor variable.

Change-Id: I02ba6858fb1842f911d62976f4c54afc3bfa337f
hidpi: Forgotten logging.

Change-Id: Ifd71f5e15ce0627f3aefd8775e588bfaf746351f
hidpi: Use the default scaling algorithm.

We are not on _that_ time critical path when setting up images for the UI, so
let's have at least some quality there :-)

Change-Id: I0a82106b0d60ac6a543d5e55c48fc86b6d5f60b1
hidpi: Add a FIXME.

Change-Id: Ia89679c832d98b5b46eeb088ed8ae4d66575e6d4