Player: Add minimizing gesture recognizer

This merge request adds:

• A minimizing gesture recognizer to the media navigation bar allowing the user to minimize the player
• An extension in order to retrieve the display's corner radius, that is used in the audio player's view.

This merge request also brings an adjustment to the presentation of the players:

• Both the video and audio players are presented over the current context meaning that when the minimizing gesture will be performed, the user will be able to see the parent view controller instead of a black screen.
• The mini player is also dismissed when the player enters the fullscreen mode in order to make the animation smoother.

Minimize_-_audio Minimize_-_video