PlaybackSpeedView: Properly notify and update values changes

This merge request brings a fix to:

• The playback speed view that is now properly updated when the playback speed is changed outside the view.
• A notification is also sent when the reset actions are performed.

Fixes regarding the playback speed shortcut of the audio player have also been made, including:

• A notification that is now sent when the playback speed is changed via the shortcut in order to properly update the views concerned by this.
• The options navigation bar that is also properly updated, following the behavior of the playback speed view.

Closes #1754 (closed)