Fix to Missing Plots at Python Lesson

This fix #402.

In this PR I don't update the markdown files generate from IPython Notebook.

~~~
$ make site
$ git diff --name-only
intermediate/python/01-intro-python.md
intermediate/python/02-modularization-documentation.md
novice/python/01-numpy.md
novice/python/02-func.md
novice/python/03-loop.md
novice/python/04-cond.md
novice/sql/01-select.md
novice/sql/04-calc.md
~~~

I don't update the markdown files because I don't like very much the path to the plots:

~~~
$ git diff -- novice/python/01-numpy.md | head -n 15
diff --git a/novice/python/01-numpy.md b/novice/python/01-numpy.md
index e87745d..f02ecba 100644
--- a/novice/python/01-numpy.md
+++ b/novice/python/01-numpy.md
@@ -577,7 +577,9 @@ pyplot.show()</pre>
 </div>
 
 <div class="out">
-<pre></pre>
+<pre>
+<img src="../../novice/python/01-numpy_files/novice/python/01-numpy_74_0.png">
+</pre>
 </div>
 
 ~~~

I try to improve the path to the plots but have some troubles due ipython/ipython#5529. I want to wait some time for comments in IPython issue before go ahead with this PR.