[INTERNAL] PaletteRoots: Replace construction with factory

The second step (not counting the refactoring) replacing the old palette
with a new one. Introduce a subclass to PaletteRoot,
WhiteboardPaletteRoot, and a factory, which in the future will do all
the palette configuration.

Adapted from SWTP-2013 repository.
 - Commit: fcb9a47
 - Reviewed on: http://saros-build.imp.fu-berlin.de/gerrit/1006
 - Reviewed-by: Richard Möhn <richard.moehn@fu-berlin.de>

Change-Id: If395ddf6fa85e4a210a29176fb738aa41b906406
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1745
Tested-by: Jenkins CI
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Reviewed-by: Damla Durmaz <ddurmaz88@gmail.com>
Reviewed-by: Arsenij Solovjev <xeper000@gmail.com>