Introduce assert exceptions codes standardisation

[jevgenika]

Make the output of errors not in text form, but in the form of a numerical value. Each error should had its own type as http error codes

[kotbegemot]

@jevgenika In which places do you want to see http code?

[nemothenoone]

The solution is to refactor new exceptions definition system introduced in #177, and to make the what-message include the exception code. The exception code gets explicitly defined right in the exception definition.

[jevgenika]

https://github.com/GolosChain/tolstoy/issues/469