platform (android): open_url now tries to open the right activity for any URL: media type is guessed (by Python standard mimetypes lib then Android API) to try to open the right intent, before defaulting to generic open_url.

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