Convert external images to PNG data URLs even if they are PNG already

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37367 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Code cleanup

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37368 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Moved classes around to make WebSimple compile again

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37369 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e