Added ability to override zeroclipboard config properties via ngClipProvider

I needed to change zeroclipboard z-index so I forked this project for me.

With this change you can override zeroclipboard config properties like this:

    ngClipProvider.setConfig({
        zIndex:50
    });

Please feel free to merge this pull request if you think this is acceptable method and make sense.
Can you please fix the indentation issue (one blank is missing) and also remove the whitespace between config and the colon ?