zoom: default back to zoom_to_mouse=True
zoom: default back to zoom_to_mouse=True

now that zoom_to_mouse is sane again activate it by default
it is much more intuitive for user

Revert "fix the default zoom behavior"

This reverts commit def778932001559d5213502d51bc1b49bcc1245e.

tommy-u/chaco,tommy-u/chaco,ContinuumIO/chaco,burnpanck/chaco,ContinuumIO/chaco,burnpanck/chaco,burnpanck/chaco,ContinuumIO/chaco,ContinuumIO/chaco,tommy-u/chaco