Adding new field to account objects

[abit]

If you're running your own chain, it's flexible to change many things. However, if you want to change the BitShares chain, it requires consensus, since blockchain by nature need all nodes to agree on all transactions, if you change your node or wallet only, it's useless.

[xeroc]

you need to extend the `account_update` operation, too to actually store stuff on the blockchain.

[dmantis]

We'd like to experiment with BitShares blockchain and research the possibility of extending accounts objects with with additinal fields.

We have tried to extend account_create_operation fields in wallet.cpp and add field in account_object.hpp abd have some success writing data to blockchain but we can't to get it back via wallet or RPC API.

Moreover, we see the extention struct, but there is the lack of documentation about it. Is it expected to be used in such cases?