Implement a cross-build mechanism for WebView similar to the cross-build in Glass and Prism.

This should be done in a way that can support cross-build for other platforms than just BeagleBoard.

"ant cross-build" builds for three different platforms, named "arm-ti", "arm-raspberry-pi" and "arm-fsl". What we do in other platforms is to build Java files only once, but to have a separate build directory for each platform so that it is possible to build for all platforms in a single repository.

The property "cross.platform" specifies the target platform.