Merge branch '2291-mailbox-upload-worker' into 'master'

Mailbox upload worker

Closes #2291

See merge request briar/briar!1673

bramble-api/src/main/java/org/briarproject/bramble/util/IoUtils.java

@@ -40,7 +40,7 @@ public class IoUtils {
 		}
 	}
 
-	private static void delete(File f) {
+	public static void delete(File f) {
 		if (!f.delete() && LOG.isLoggable(WARNING))
 			LOG.warning("Could not delete " + f.getAbsolutePath());
 	}