Upgrade to Matplotlib 1.5

If we are to integrate with allen-SDK, we should have matplotlib > 1.5.0
The current Matplotlib HTML5 backend that we are maintaining is not compatible with the newest matplotlib API.

• _png.write_png change signature
• Image.flipud_out has been removed and we need to do it in a numpy representation

Attached we have the required fixes for TVB to work with Matplotlib 1.5.
As we do to maintain an if in the code with different calls based on matlab version, we should update the matplotlib installations on the build machines before committing this.