MEP22 Navigation toolbar coexistence

This version of the MEP22 implementation https://github.com/matplotlib/matplotlib/wiki/Mep22#implementation 

The proposed solution is to take the actions out of the `Toolbar` and the shortcuts out of the `Canvas`. This actions and shortcuts will be in the form of `Tools`.

A new class `Navigation` is the bridge between the events from the `Canvas` and `Toolbar` and redirect them to the appropriate `Tool`.

Nope, not straight away, due to the missing .so, so I either need to build somehow, or cheat, I shall go through one by one and ``ln -s`` them in and hope for the best.   I run from debian using ``PYTHONPATH=/path/to/git/repo/dir/lib python navigation.py``.