Big charts refactor

WIP, mostly to avoid working in the solitude :stuck_out_tongue:... but NOT for review yet.
This makes be think, @damianavila, why this way? Everywhere in bokeh we use keyword arguments. Is there a reason to switch to this new style or you just found it more appealing? I use similar style in bokeh-scala, but that's mostly from necessity (due to type-safety and possibly immutability in future).