PyBackgroundThread test.  5,000 keys/s with 4 threads

Crypto++ is slow, but it parallelizes well with standard python
threading.  Get about 1,200 keys per sec, raw priv-->pub computation
using the CryptoECDSA().ComputePublicKey() method.
Fixed a ton of bugs (and suboptimal features) from subSTRATA

Fixed/updated:
Being able to save empty offline transactions
Remove error highlighting on Send-BTC window when modified (HACK!)
Disabled all paths to get to Send-BTC window when offline/scanning
Refresh the wallet-address list immediately after addr book operation
Changing wlt labels caused \x00 bytes show up in "Backup Indiv Keys"
Delete private-keys-only-make-WO-wlt gives appropriate warning