Add state events

[mezrin]

If we will try to create really fast API of a blockexplorer - we will face a problem: in order to read smth from the contract state - we have to call getter of the contract.
I.e. we have to launch Ethereum virtual machine and execute the contract.
It is not possible to cache such data in the blockexplorer.
A possible solution - save state in the events.
For example, when user transfer tokens - we save in the events not only addresses of sender&receiver and transferred amount, but also new balances of each of them.

• Think about this
• Estimate gas costs
• If we agree with this solution - implement