Do not inject self in IPython namespace

And do not require namespace either

  - this is bad practice, and this prevent from
    writing a blended content manager that works both
    with drive and localhost as they should both export
    themselves to `IPython.Contents` module.


If we really want `IPython.Contents` then the various `main.js` should set `IPython.Contents` to the `Contents` they import. 

Though it is unnecessary as one can still do `C = require('contents')` for the global content manager or even `var c = require('explicit/module/path')`
As I understand it, in order to make this syntax work, require has to do some kind of madness where it finds these statements and rewrites them to the function call form before executing the code. Not sure that I'm entirely comfortable with that.