0.0.43 release

 - Removed touch vibration feedback completely
 - Voucher messages
 - Safer external/social transaction URLs (private key in # hash part, not sent
   to server anymore)
 - Disallowed external transactions below 0.1543mBTC to make sure enough money
   is available for anti-dust rules and redemption fee
 - Double spending detection
 - Buttons in transactions list to regenerate old vouchers
 - Modal dialog for redeeming external transactions from transaction list
 - Fixed mnemonic encryption in signup
 - Fixed zxing plugin storing mnemonics in history
 - Other minor improvements