Versionized Account

[marco-sundsk]

First commit

• Versionized Account；
• leave storage_used field in Account;

Note: The following second commit has been reverted. leave it for independent branch and PR in future.

Second commit

• The whole storage management logic upgrades to storage_used way to trace real usage of storage of each user;
• Now, all register_token, add/remove liquidity, register mft, add_pool and swap are recorded by storage_used and cause an Account creation if necessary;
• The side-effects is now, In-tx-refund is not supported in add_pool, add/remove_liquidity, mft_register actions. Cause, all attached deposit would be added into account.near_amount, user can storage_withdraw leftover amount later.