NEW: check changed state text fields on keyup, rather than just change

This issue relates to the state of the save/publish buttons in CMSMain. They only update on blur of the text fields, creating an awkward UX, since many users will click one of those actions whilst the text fields are focused.

Minor: update changetracker to use on() and off() instead of bind() and unbind().
Can you document that `input.changetracker` in this context refers to the (relatively new) `input` event scoped to `changetracker`, Its easy to misread this as a CSS selector. You could also highlight why its necessary: fires on paste as well as keyboard input.