chat: use `image-loading` as source by default: not specifying source was resulting in graphical glitches (notably when the image could not be downloaded correctly). Using `image-loading` as default avoids this, and indicates to the user that something is running in background.

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