add sqlc, fix background img fetching

grpc-backend/sqlc/query/collection.sql

@@ -0,0 +1,42 @@
+-- name: InsertCollection :exec
+INSERT INTO Collection (Name, MD5Hash) VALUES (?, ?);
+
+-- name: GetCollectionCountByName :one
+SELECT COUNT(*) FROM Collection WHERE Name = ?;
+
+-- name: GetCollections :many
+SELECT c.Name, COUNT(b.MD5Hash) AS Count, MIN(b.Folder) AS Folder, MIN(b.File) AS File
+FROM Collection c
+JOIN Beatmap b ON c.MD5Hash = b.MD5Hash
+WHERE c.Name LIKE ?
+GROUP BY c.Name
+LIMIT ? OFFSET ?;
+
+-- name: GetCollection :many
+SELECT 
+  c.Name, 
+  b.BeatmapId, 
+  b.MD5Hash, 
+  b.Title, 
+  b.Artist, 
+  b.Creator, 
+  b.Folder, 
+  b.File, 
+  b.Audio, 
+  b.TotalTime
+FROM Collection c
+JOIN Beatmap b ON c.MD5Hash = b.MD5Hash
+JOIN (
+  SELECT DISTINCT Name
+  FROM Collection
+  ORDER BY Name
+  LIMIT 1 OFFSET ?
+) selected_name ON c.Name = selected_name.Name
+LIMIT ? OFFSET ?;
+
+-- name: GetCollectionByName :many
+SELECT c.Name, b.BeatmapId, b.MD5Hash, b.Title, b.Artist, b.Creator, b.Folder, b.File, b.Audio, b.TotalTime
+FROM Collection c
+JOIN Beatmap b ON c.MD5Hash = b.MD5Hash
+WHERE c.Name = ?
+LIMIT ? OFFSET ?;