NF - Left and right side axes titles

Add left and right side titles to axes, in addition to the existing title which is in the center.

There are many instances in which one would like to display title on the left and right sides of the top of an axes rather than in the center (e.g., title on the left side and some relevant statistic on the right side). This PR adds two new titles to matplotlib axes to allow this (in addition to the existing title functionality).

A quick example:
![lrtitles](https://f.cloud.github.com/assets/390602/49881/d601c1e8-5981-11e2-80c6-e12e10cc2f5c.png)