Add rejected transactions to DAG.

[bartossh]

Transaction issued to the C9s network may be in three states:

• (Data state) Only contains Data and no Tokens.
• (Tokens state) Only contains Tokens and no Data.
• (Mixed state) Contains Data and Tokens.

The receiver must confirm the data state transaction and after it is confirmed or rejected it is added to the DAG. If the Transaction has no receiver signature and has no empty data it is considered rejected.
The receiver mustn't confirm the token state transaction, the transfer of tokens will happen only with the issuer's signature.
The mixed state combines the above, lack of receiver signature rejects the data bu token transfer requires only a valid issuer signature.