Update Axes3D.tricontour for custom triangulations

An example has also been added to illustrate the additional flexibility
possible with providing a user-defined triangulation.
Make Axes3D.contourf take arbitrary triangulations
Add Axes3D.contourf example
Update changelog/whats_new for 3D tricontour plots
Typos
Add EXPERIMENTAL note to Axes3D.tricontour[f] docs
add extra keys to qt4 backend
support for unicode key_press_event
comments
pull qt keys into module variables
add tests for Qt Key handling
simplify key getting logic
expose modifier key indexes
fix tests
remove unused text() from qt key testing
backspace tests
parens for clarity
require mock
compare python versions correctly
Tests reports found version of nose/mock