Some fixes and integration of Safari view controller

[kirb]

• Fix bad case on External/usr/include/JavascriptCore filename: For weird people like me who use a case-sensitive filesystem. The JavaScriptCore includes were using the headers from the SDK instead of the headers in this project.
• Add URI scheme back to Info.plist: Allows cydia:// to be tested via simctl: xcrun simctl openurl booted 'cydia://search'
• Use Safari view controller for target="_open" requests: Not sure if _open is properly documented anywhere, but it launches Safari for the url rather than opening within the app. As it's expected by users now, and because it's functionally the same, launch a Safari view controller instead of using openURL: where it's available (iOS 9.0+).

[JohnCoates]

I've committed the bad case and the Safari VC. The Info.plist commit will be left out for now since it would conflict with Cydia's URI scheme. Possibly change to limitless://?