v3: allow users to edit dump thumbnail, fixed some linter errors in the frontend

api/db/schema.sql

@@ -14,6 +14,7 @@ CREATE TABLE dumps (
   file_size   INTEGER,
   vote_count  INTEGER NOT NULL DEFAULT 0,
   is_private  INTEGER NOT NULL DEFAULT 0,
+  custom_thumbnail_mime TEXT,
   FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
 );