ipython: fix --pylab mode

"ipython --pylab" currently fails because it cannot find matplotlib. Fix
that by adding matplotlib and pyqt4 as dependencies. (pyqt4 is needed
for interactive plotting; the default 'agg' backend only writes to
file.)

Also:
 * modularize the expression with new attributes (all default to true):
     notebookSupport
     qtconsoleSupport
     pylabSupport
     pylabQtSupport
 * add missing jinja2 as dependency for "notebook" support (now
   controlled with the notebookSupport attribute)