When `player.reset` is called the `titleBar` component is not reset.
- Sets the properties `title` and `description` to `undefined` when `player.titleBar.update` is called so that the component is properly reset.
When `player.reset` is called, the `errorDisplay` component is not reset, and neither is `player.error`.
- Sets `player.error` to `null`, so that the `player.errorDisplay` and `player.error` are correctly reset.
- Adds an `error` function to the `testPlayer` stub to prevent tests from failing.
The resetProgressBar_ method was calling 'updateContent' on the durationDisplay and remainingTimeDisplay controls without checking to make sure they exist
Fixes#5838
