Refactor Recorder to be Session and SessionsFactory

[wroscoe]

One of the most common and laborious tasks of building a self driving car is saving and accessing data for different trial sessions. Currently this is accessed through the FileRecorder. This is not a clear way to represent the access of the data.

A much cleaner way would be to use Session objects with uses cases like:

sfactory = SessionFactory('~/sessions')
session = sfactory.new('port')
for i in records:
    session.record(r[img], r[angle])

X, Y = sesssion.array()