add `to_notify` param to actions

[DenisCarriere]

add optional to_notify param to the following actions:

• [x] destroy
• [x] generate

// @user
[[eosio::action]]
int64_t generate( const name owner,
                  const bool bound,
                  const uint32_t amount,
                  const string data,
                  const optional<name> to_notify);