MEP22 Navigation toolbar coexistence TODELETE

**Edit**
This PR has been dropped in favor of https://github.com/matplotlib/matplotlib/pull/3652


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`.