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')`
Readability more simple to refactor after, diminish conflicts if several people remove/add requirements. Does exactly the same than `require([list, of, module, name], function(same, name, as, before))` except you get the local name of the module and the actual import on the same line. and it requires  the signature of the only arg of the function to be name `require`.