Android addJavascriptInterface meterpreter

The addjavascriptinterface returns a shell session, however it's not easy to upgrade that session to meterpreter without dropping a root exploit. After these changes it drops a JNI stager which loads a meterpreter session within the vulnerable application. The javapayload pr is here: https://github.com/rapid7/metasploit-javapayload/pull/9

- [x] use exploit/android/browser/webview_addjavascriptinterface; exploit
- [x] navigate to the url on a vulnerable Android device/browser
- [x] a meterpreter session will be opened instead of a shell session
- [ ] webcam_stream should work if the exploited app has camera permissions (most do)