For markers (resize markers, anchors,...) we contain them all in
one image atlas. This was generally done because of resource
limitiations in Windows 95/98 which aren't a problem anymore in
present systems.

This is however problematic in HiDPI as we scale the image and
the coordinates of aren't correct anymore. Another problem is
that it uses its own cache instead of common cache in
ImplImageTree. So this commit extracts all the markers into its
own images for galaxy theme and uses them when we scale.

In the future when we extracted all the markers to its own
images for all icon themes we can remvoe the old code with the
image atlas.

Change-Id: Ibee181b529d30e20050df8cd396d338bd53532c0