Async/Awaited all db methods

This is a rather large PR which updates the async branch to have all the
database methods as an async fn.

Some iter/map logic needed to be changed to a stream::iter().then(), but
besides that most changes were just adding async/await where needed.

src/api/icons.rs

@@ -745,6 +745,7 @@ async fn download_icon(domain: &str) -> Result<(Bytes, Option<&str>), Error> {
                     buffer = stream_to_bytes_limit(res, 512 * 1024).await?; // 512 KB for each icon max
                                                                             // Check if the icon type is allowed, else try an icon from the list.
                     icon_type = get_icon_type(&buffer);
+                    // Check if the icon type is allowed, else try an icon from the list.
                     if icon_type.is_none() {
                         buffer.clear();
                         debug!("Icon from {}, is not a valid image type", icon.href);