shortened python sessions

From our last meeting I understood that we wanted to try to fit the python sessions in the afternoon of the first day.
This pull request is my attempt so far. We don't have to merge this. I can make changes on what we discuss at the meeting today.
I combined the sessions variables and data structures into writing code for people for the 1:30-3:00 session. 
I combined the sessions flow control and functions & modules into dont repeat yourself for the 3:15-4:0 session.

Since the Readmes are in new folders and combinations of to files the diff view isn't helpful. 
In the first session I removed the theory of coercion and file i/o (covered in session 2). I also grouped all the string and int / float operations together.
In the second session I shorted some of the codes. I probably didn't cut enough to be able to get through the implant example at the end.