Create a shared interface, MOAIBrowser for opening urls across platforms

Addresses issue #514 by doing the following:
* Move MOAISafariIOS to MOAIBrowserIOS
* Move MOAIAppAndroid::openURL to the newly created MOAIBrowserAndroid class
* Add openURLWithParams to Android

This PR also addresses PR #413 by adding the method canOpenURL to both platforms.

Please close both of these tickets when merging this PR.  Thanks!