fix(carousel): #488 Carousel fails to update model changes.

Fixed carousel to update the carousels isolate scope when a slides ng-repeat $index has changed e.g. with orderBy filter.

Created new PR due to fix being made to outdated version in PR #1969. However I would like to continue the discussion of the issue brought up about using $index by @chrisirhc and users not using the ng-repeat directive for their slides. My question was if is this an issue due to the fact that they are managing their slide manually, at that point would there be an expectation for updates to changes to the order of these? If that is a valid expectation, what would be the best method for watching for these changes? e.g. a watcher on the entire Carousel DOM.