Store each client's play queue in the database

The queue lived in memory and was shared by all clients, so a restart or a
finished sync cleared it. Every client now has its own queue in the new
queue and queue_song tables (added to the undeployed migration 000006).

The music endpoints return the queue ID in the X-Queue-Id header and expect
it back. A request without an ID, or with an ended one, starts a new queue.
/music/reset ends the queue and returns a new ID, and a sync ends all
running queues. Ended queues are kept as history.

The deprecated legacy routes without the /api/v1 prefix are removed.

internal/db/migration_integration_test.go

@@ -65,7 +65,7 @@ func TestMigrationsKeepData(t *testing.T) {
 	assert.Error(t, err, "game table is renamed")
 }
 
-func TestFingerprintMigrationDown(t *testing.T) {
+func TestFingerprintAndQueueMigrationDown(t *testing.T) {
 	database := openDatabase(t, pgtest.NewDatabase(t))
 	m, closeFn, err := database.NewMigrator()
 	require.NoError(t, err)
@@ -75,6 +75,8 @@ func TestFingerprintMigrationDown(t *testing.T) {
 	require.NoError(t, m.Steps(-1))
 	assert.Equal(t, 0, count(t, database,
 		"SELECT COUNT(*) FROM information_schema.columns WHERE table_name = 'soundtrack' AND column_name = 'fingerprint'"))
+	assert.Equal(t, 0, count(t, database,
+		"SELECT COUNT(*) FROM information_schema.tables WHERE table_name IN ('queue', 'queue_song')"))
 	require.NoError(t, m.Up())
 }