Make chaco demos Qt compatible.

Update examples to run on Qt. Before this change, the demos gave tracebacks in the IDE.

~~This is not ready to be merged! In the IDE, the `updating_plot` demos will run for a while and then crash the kernel.~~

This PR requires https://github.com/enthought/enable/pull/92
This PR includes a workaround for https://github.com/enthought/enable/pull/95