Add colours for charts.

as per issue #842 I've added the colours specified by
@cfarquharson to the /grids/sass/_mixins.scss for want of a
better place to put it.
Added column-* CSS to design guide
Merge pull request #1119 from cfarquharson/master

Added column-* CSS to design guide
Merge pull request #1110 from CalvinRodo/chartcolors

Add colours for charts.
Merge remote-tracking branch 'upstream/master'