Composite

Hi Tom,

Today, I was requested to add compositeChart support for angularDC.

While working for that, I was annoyed by the fact that the build system does not have live reload, karma was failing, and so on so I also moved the build system to gulp and guanlecoja, which has all the nice modern features.

I just finished the declarative compositeChart is working, its eventually a few lines of code in angular-dc (I was planning that this would require a much more complex directive setup, but it eventually went simple)

So please let me know if you want me  just contribute the feature, or if you find it can be useful to use guanlecoja.