Modify bundling to create universal dev_bundle

Builder for an universal dev_bundle to run meteor also on different architectures like ARM.
This universal bundle is able to use pre-installed platform binaries for node and mongo.
Run meteor inofficially on ARMv6l and ARMv7l architecture like RaPi and UDOO and others.
Update README.md

Add infos about unsupported architectures and build for universal bundle. Change git url to our patched default tree.