User can change the image of turtle in properties panel - started.(#4721) Image of turtle already visible and moves with turtle, but won't turn with turtle yet, won't be saved, and won't be rescaled.

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37465 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e