Changed ONS charts code

Fixed y axis label;
Change filled polygon to line chart;
Allows custom colour to be set via data attribute in html
Google fonts: used relative protocol
Google fonts: Changed all to relative protocol

Also tidied up CSS declarations
Merge pull request #12 from mcoulthurst/master

Updated charts code to display lines not fills
Tidied up html
Amended LineSingleN

Fixed y value labels for wide line chart that I broke;
Updated chart display for single lines to use max and min values and
also display negatives;
Added Article page

Also added link to menu for other pages
Merge pull request #13 from mcoulthurst/master

Article page plus chart amends
Merge branch 'master' into gh-pages