Player: Swipe to minimize

This patch adjusts the distance you have to swipe to minimize the player from 50% of the view height to 10%, making it significantly easier minimize the player.

This patch also makes it so that you can swipe down from the middle of the screen to minimize the player. If the volume/brightness gestures are disabled, you're able to swipe down from anywhere on the screen.

Before:

After:

Forward-port from: https://github.com/videolan/vlc-ios/pull/456