Fix hack I added to test RTL display
2465: "middle-focus" behavior

- When a subtitle is shown on the timeline, scroll to it
- Don't scroll to a subtitle we are in the middle of an edit
2465: Give current subtitle a blue background.

Added timeline model to the app controller.

Extended the subtitle-repeat directive once again to accomplish this.
This directive is kindof getting out of control, we should really
replace it with something that lets us run arbitrary angular
directives.
2550: editor key shortcuts