CSS adjustments

- remove boilerplate.css, as it is redundant with bootstrap's own reset.less
- add ipython.less / ipython.min.css for IPython-only CSS
- move font-awesome to outermost style.less, so it is not included in ipython.min.css,
  where it is not desirable.

This doesn't do any of the naming / scoping cleanup that we should ultimately do, but it does create the file where that will have its desired effect.

Ping @jakevdp for comments on how well ipython.min.css actually plays with embedding in other environments.