2 new commandline arguments: --clipin and --clipout

[8go]

Added 2 new features, implemented as 2 new command line arguments:

• --clipin: similar to --stdin, reads arguments from clipboard
• --clipout: for selected commands writes output additionally to clipboard
• example use case: hwi -t $DEVICE --clipin --clipout signtx # works well in combination with e.g. Bitcoin Core wallet