cagou widget: don't add header_input systematically anymore: header input is often used in CagouWidget for e.g. filtering, but not always, and when it is not, it is weird and confusing to have a TextInput which doesn't do nothing. To avoid that, a new `use_header_input` bool attribute (set to False by default) has been added to CagouWidget.

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