Object Versioning: working source maps for transformed code

the UglifyJS code generator is configured to also generate a source map,
which is then enriched with the original source code and appended to the
generated code using a data URI

see lively.versions.UglifyTransformer.generateSourceFrom(url),
inspired by http://kybernetikos.github.io/jsSandbox/srcmaps/dynamic.html
Object Versioning: transformed sources shown in correct directory

added correct directory as sourceRoot property of source maps
when transforming code loaded from an URL
Object Versioning: transform code from URL or eval scripts
Object Versioning: cleaned up generation of code + source maps