message: add function to retrieve the wallet tag
diff: @@ -115,6 +115,10 @@ impl Blockchain {
  let tag = format!("wallet/{}", wallet_name);
  tag::remove_tag(&self.storage, &tag);
  }
  + pub fn get_wallet_tag(&self, wallet_name: &str) -> Option<block::HeaderHash> {
  + let tag = format!("wallet/{}", wallet_name);
  + tag::read_hash(&self.storage, &tag)
  + }
  pub fn load_tip(&self) -> (BlockRef, bool) {
  let genesis_ref = (BlockRef {
  