Fix `safeAreaInsets`

Use safeAreaInsets of window to avoid wrong insets caused by toolbar/tabbar.

Expose `safeAreaInsets` in STPopupController

• Expose safeAreaInsets so that it could be overridden to 0 in some use cases.(#125)
• Restore transform when laying-out container view to avoid unexpected value.

Duplicate of 1.8.4

Duplicate of 1.8.4
This is a redundant release. You should use 1.8.6 instead.

Fix Several Layout Issues

• Take safeAreaInsets into account when popup is presented as bottom sheet(#102).
• Fix layout issue when navigationItem.titleView is used(#115).
• Adjust position if contentSizeInPopup is changed in the middle of keyboard animation.
• Fix navigationItem.rightBarButtonItem layout issue when orientation is changed.

Fix Title View Animation Issue On iOS 11

• Fix title view animation issue on iOS 11 (#101)

Translate Origin Of Container View To Be Vertical-Centered If There Is Enough Space

Translate origin of container view to be vertical-centered if there is enough space.

Swift Friendly

Added nullable annotation to be Swift friendly.

Support Custom Transition Style of Popup

• Support custom transition style of popup by providing STPopupControllerTransitioning protocol.
• Fixed #74.

Bug Fixes and Transition Tweak

• Fixed #34 #62
• Tweak vertical slide transition animation.

Bug Fixes and "hidesCloseButton"

• Fixed #63 .
• Added "hidesCloseButton".
• Transition animation tweaks.