Introduce Promises to make reading code easier

Hi,

not sure if this is a topic you are interested in, but I tried to cleanup the callbacks a bit by introducing Promises and the Bluebird library ( https://github.com/petkaantonov/bluebird ).

Feel free to give critical feedback or close if it is not relevant right now. I was wondering that it might help to track problems with finding the right files easier.

Thanks for your interest!