Fixes for the bug where the PriorityHub view would not dismiss after dismissing notifications by swiping down notification center

From the small blurb I added in the code:

v1.1.1 of this tweak has/had a bug where if a user tried to dismiss a notification by swiping down the NC, the NC would stutter and refuse to open on the first try, then open completely on the second try and dismiss the notification, but leave the PriorityHub view on-screen. Hooking the methods `hostWillPresent` in `SBNotificationCenterViewController` and `presentAnimated:completion:` in `SBNotificationCenterController` (both called when the NC is presented) prevents this issue.