Updates for newest Crosswalk integration API (6.35.124+)

The lastest Crosswalk code (as of crosswalk-project/crosswalk@1939881) has removed the `XWalkResourceClientImpl` and `XWalkUIClientImpl` classes. This patch gets cordova-crosswalk-engine working with the newest release. (It breaks compatibility with Crosswalk 6.35.123 and earlier, though)