remove ImagePreview (unused, now part of GeoGebraFileChooser)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36381 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fix click coords in spreadsheet when software zoom

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36382 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e