Include Chainstate in checking Transaction validity

[thepiwo]

• check if one account from the chainstate has enough balance available that should be spend in the transaction, if the balance minus the available balance is below 0 the transaction should be considered invalid
• check validity when mining considering the transactions to be added to the new block, to do so use a temporary clone of the chainstate when checking each transaction and add each transaction there. The issue could be that there are more transactions originating from one account inside a block to be mined that when added up exceed the accounts balance, in this case the first transactions not exceeding the balance are considered valid, the others invalid.