ReactART, Perf Monitor, PushNotifications and RN@0.26.0

Some breaking changes:

• respondsToLiveResize not enabled by default;

Features:

• Added systemImage option for <Button /> 8a97563
• Perf Monitor! 12fb655
• ReactART! db6ee6f
• Hotkeys for DevMenu a228e4f
• Basic support for localNotification (PushNotificationIOS) c0f0b2d;

A bunch of bugfixes (thanks for @genbit and @beretboat).