Add minting info icon and nicer unlock interface

Added minting GUI icon.
Replaced ugly unlock button with a nicer one.
Added menu items to lock/unlock wallet.
Added option to unlock for minting only.
Updated licence authors.

The previous commit adds code that came from blackcoin. Update COPYING
to include the same authors as blackcoin's licence.
Merge remote-tracking branch 'upstream/master'
Fix GUI lagging when client is syncing.
Merge pull request #14 from skwurp/master

Add minting info icon and nicer unlock interface