Address a few more review items.

- Distinguish between missing address and database error
- Wrap help text for wallet generation seed
- Don't rescan if there are no addresses
Added account name index
Lookup account by name and start updating RPC calls
handle invalid account name
don't add index entry for default account
updated getaddressesbyaccount to use accounts
updated getaccount to return address account
updated getreceivedbyaccount to filter by account
updated getbalance, getunconfirmedbalance to filter by account
Index addresses by account
update listtransactions to filter by account
update listalltransactions to filter by account
update GetAccount to return account name
updated ListAccountTransactions to include sent tx
update sendfrom, sendmany to use accounts
updated listaccounts to return all accounts
fetch account name in validateaddress
updated listreceivedbyaccount to list all accounts
updated listreceivedbyaddress to use accounts
added bucket and methods to read/write enc cointype keys