core: handle URLs opening in a per-platform way: URLs opening may have to be done in a different way according to platforms, so an `open_url` method has been created in base Platform which can be overriden.

<intent-filter>
    <action android:name="android.intent.action.SEND" />
    <category android:name="android.intent.category.DEFAULT" />
    <data android:mimeType="*/*" />
</intent-filter>