fix different iOS version get keyWindow issue.

Fix crash: When delete datasource and reload data cause crash. Refer: https://github.com/HeathWang/HWPanModal/issues/103 https://github.com/HeathWang/HWPanModal/issues/107

add new API:

/**
 * call this method to dismiss your presented VC directly
 */
- (void)hw_dismissAnimated:(BOOL)animated completion:(void (^)(void))completion NS_SWIFT_NAME(dismissAnimated(animated:completion:));

bug fix

- (BOOL)allowsPullDownWhenShortState;

improve allowsTouchEventsPassingThroughTransitionView api