Merge pull request #37 from mdr0id/reorg_logic1

Use REPLACE on db row creation for initial reorg logic

storage/sqlite3.go

@@ -122,7 +122,7 @@ func GetBlockRange(ctx context.Context, db *sql.DB, blockOut chan<- []byte, errO
 }
 
 func StoreBlock(conn *sql.DB, height int, hash string, sapling bool, encoded []byte) error {
-	insertBlock := "INSERT INTO blocks (block_height, block_hash, sapling, compact_encoding) values (?, ?, ?, ?)"
+	insertBlock := "REPLACE INTO blocks (block_height, block_hash, sapling, compact_encoding) values (?, ?, ?, ?)"
 
 	tx, err := conn.Begin()
 	if err != nil {