Stop redrawing graph on each expression change.

Check the typeahead performance on this @juliusv. I realized this weekend that `redrawGraph` was being fired each time an expression changed, which would explain the poor performance. I also don't see any reason for that to be there, right?
Selecting an axis currently requires a manual refresh. Even when adding in a watcher for a change to the `axis_id`, and confirming that `redrawGraph` is executed, a manual refresh is still required for changing the axis on an expression to be rendered. Which is odd.