change validate-address operation contract

Current implementation is not safe in a sense that the operation fails if the address is not valid. There is no safe way, i.e. a boolean result, not a failure, to check whether an address is valid.
The idea is to change the current validate-address so that:

• it's only a root operation, not inherited like the current impl;
• add an address argument (the current impl has no arguments), which will be the address to check;
• the result type should be a boolean value;
• in case of failure, include a message into the response describing which part of the address is wrong.