Implementing #4: Copies key to clipboard on click using ZeroClipboard.

Implementing #4: Copies key to clipboard on click using ZeroClipboard.

ZeroClipboard is also used by GitHub.

Tested in Firefox, Chrome and IE11. But ZeroClipboard (https://github.com/zeroclipboard/zeroclipboard) says it would be supported by IE9+ and inofficially also on IE7 + 8.