player: Synchronize Player and PlayerPlaylist repeat_mode

There are two ways to change the repeat mode. First, from the PlayerToolbar. This change triggers the 'changed::repeat' signal of the PlayerPlaylist which updates its repeat_mode property. It also updates Player repeat_mode property because of a binding. However, this binding is unidirectional. It is also possible to change the repeat mode by using shortcuts (for example Ctrl + r). This updates PlayerPlaylist repeat_mode property but not the Player one as the binding is unidirectional. Therefore, the player toolbar icon is not updated.

Make the binding bidirectional to fix this issue. Create the binding at instantion time because it does not need to be updated when a playlist changes.