This adds a new interaction mode to vtkChart which zooms the
X and Y axis based on the X and Y movement of the mouse. This
is similar to the zoom mechanism in matplotlib.

This also adds some documentation for the mouse actions enum in
vtkChart along with a test for the new ZOOM_AXIS mode.

Change-Id: If6c923607a3bf86ec8f6bc16188d1e49a260ba95