* Added ability for extension to be applied to non-SiteTree objects by moving the `isAPage()` check in to the `showBetterNavigator()` method, which can be overidden.
* Added ability for edit link to be enabled via a permission code check, configurable on a per-controller basis.
* Switched to using getField/setField for caching whether better navigator should be displayed or not.
* Adjusted readme around using custom logic to control the display of the navigator.
In the situation that a user has draft site access but no CMS access they received a '$editLink not defined error'. This corrects that by defining it as false.
In use with Silvershop, a form post from the AddProductForm would pass the form trough the `afterCallActionHandler` as the `$result`. This causes the `getValue` to error. By checking if the result is an instance of `DBHTMLText` this error can't happen anymore.
