Remove old ggplot support

OK, and because PR are free, and a good point to start a discussion, this is my proposal:

* Remove old ggplot support.

Reasoning:

* We have invested (we re investing and we plan to invest) time in developing mpl support for Bokeh... and mpl support gives us very quickly (and with little efforts) to ggplot support (and seaborn, and whatever library uses mpl under the ground)... so, it is makes no sense to me to have our own "implementation" of ggplot inside Bokeh if we are providing at the same time with another channel to do that. Also this "own" ggplot support is not being developed in the last months and I do not think we are going to spend resources on it in the future (OK, maybe I am missing some things... if this is the case, let me know...).

Implementation:
Just remove all the code :wink:, I mean:
* chaco_gg folder
* ggplot-related files in attic
* functional.py, ggploy.py and pandas_plot_data.py
* test/chaco_gg
* test/web
and a minor fix to `setup.py`. I think I don't missed any related stuff, but if I do, let me know...

Test are passing for me... but maybe I am breaking something not tested...

Finally, I repeat myself: maybe there is something useful you want to use inside some of these files... or maybe I am missing something big here... please, let me know if this is the case (PRs are free, so we can close it if anyone think this is not appropriate).

OK, just waiting for feedback... thanks!