Upcoming changes v0.9.0: upgradable wallet, domain name binding, conditionally triggered auto-recovery, recover tokens about one-wallet

[polymorpher]

Updates to upgrade mechanism, implemented in #82:

One of new mechanisms is called forwarding and back-linking. They allow the wallet to specify future payment it receives to be forwarded to another contract. It also keeps a record of backlinks: a list of 1wallets that are forwarding payments to this wallet. This mechanism allows the client to upgrade the user’s wallet by spawning a new wallet when a new version is available, and have the old wallet to forward all funds received to the new wallet.

In the PR, the backlinks are left empty - I will add another argument in the wallet constructor to set that value, as well as another OperationType.

Once wallet A is set to forward to wallet B, wallet B will have full control over wallet A, bypassing all security checks. Forward doesn’t automatically transfer wallet A's assets to the wallet B, unless wallet A's recovery address is unset (0 or default value).

To transfer all remaining assets in wallet A to the wallet B (the forwarding address), wallet A's recovery address needs to send some amount of ONE to approve the transfer. If wallet A’s recovery address sends 1.0 ONE to wallet A, all the remaining assets of wallet A will be transferred to the recovery address. If it sends any other amount, all the remaining assets will be transferred to wallet B (the forwarding address).

[polymorpher]

Done. Mechanism is slightly altered. To add documentation later.