Watch-Only Addresses: Separating Transaction Signing From Transaction Processing

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A major issue many have faced in using bitcoind to build applications is the lack of RPC support for tracking transactions and balances without having to know and keep associated private keys in the wallet. Oftentimes one might want to watch other people's transactions or to keep signing nodes behind tighter security while using separate relay nodes to service all nonsigning, non-key-generating application functionality such as sending payment and confirmation alerts.

In order to achieve these objectives, I have had to build a bunch of custom software - much of which duplicates functionality that is already present in the Satoshi Client. This pull request is an attempt at addressing some of these concerns without having to fundamentally restructure the client architecture. (Thanks, sipa!)

The proposal is to add another kind of object to the wallet database - a bitcoin address sans private key - which the client treats as if it were any other wallet adddress except for when it comes to signing and privkey export operations. This means RPC calls such as getreceivedbyaddress and listtransactions can be used on arbitrary bitcoin addresses.

I've added an RPC call:

	importaddress <bitcoinaddress> [label] [rescan=true]

The address is added as a new type of serialized object in wallet.dat and loads into the key maps of the CKeyStore instances with the key set to the CKeyID and the secret set to an empty vector.

Please test it out and let me know what you think.

Cheers,

-Eric Lombrozo