Centralise transaction committing

osu.Game/Beatmaps/BeatmapManager.cs

@@ -198,7 +198,7 @@ namespace osu.Game.Beatmaps
                         context.SaveChanges();
                     }
 
-                    transaction.Commit();
+                    context.SaveChanges(transaction);
                     return set;
                 }
             }
@@ -313,9 +313,7 @@ namespace osu.Game.Beatmaps
                     }
 
                     context.ChangeTracker.AutoDetectChangesEnabled = true;
-                    context.SaveChanges();
-
-                    transaction.Commit();
+                    context.SaveChanges(transaction);
                 }
             }
         }

osu.Game/Database/OsuDbContext.cs

@@ -93,6 +93,13 @@ namespace osu.Game.Database
             modelBuilder.Entity<BeatmapInfo>().HasOne(b => b.BaseDifficulty);
         }
 
+        public new int SaveChanges(IDbContextTransaction transaction = null)
+        {
+            var ret = base.SaveChanges();
+            transaction?.Commit();
+            return ret;
+        }
+
         private class OsuDbLoggerFactory : ILoggerFactory
         {
             #region Disposal