ipython: modularize and enable more features

Add these new attributes (all default to true):

  notebookSupport
  qtconsoleSupport
  pylabSupport
  pylabQtSupport

This adds jinja2, matplotlib, pyqt4 and sip as new dependencies of
ipython.

This commit fixes "ipython --pylab" so that it no more errors out with
"ImportError: No module named matplotlib" (which was my initial goal).