AttachmentStore now has its own runloop, can download attachments

kordophone/src/api/mod.rs

@@ -49,6 +49,7 @@ pub trait APIInterface {
     async fn fetch_attachment_data(
         &mut self,
         guid: &String,
+        preview: bool,
     ) -> Result<Self::ResponseStream, Self::Error>;
 
     // (POST) /authenticate