private keys without master keys and some fixes for things which broke along the way
skip key 0 (master) on retry for passphrase
don't cache passphrase twice
fix issue 42
remove signing icon for master keys which can't sign
tidy up code
correctly encrypt using symmetric key if sign box checked
Fix decrypt file selection and symmetric decryption failure
select correct master key for signing public key with
change how empty private cheks happen, speeds things up
use db to mark keys which can certify
only sign keys if private key has capability
change edit key for empty private master keys
use certification keys to sign keyrings
Merge with ashh87s pull request