CodeMirror 3

Totally remove codemirror from source tree and assume it is a component. 

You HAVE TO install codemirror in /static/component/ by cd into /notebook/ and issue a `$ bower install` (it will install bootstrap, less and codemirror-head in the right place) 

We need to find a way to separate dev-dependencies from running dependencis.

The rest of the PR are fixes to work with new CM version. 
Only missing thing is `?` as a single operator, which is not correctly highlighted. 


Of course this is only for test purpose, see how hard it was.

Bugs : 
  - [x] cursor position after line wrapping.
  - [ ] md cell -> md highlight
  - [ ] tooltip, increase z index (see through codemirror)