Support custom properties on themes

[Sune Simonsen]

pen.installTheme('html', {
    properties: {
       accentColors: [
           '#F44336', '#E91E63', '#9C27B0',
           '#673AB7', '#3F51B5', '#2196F3'
       ]
    }.
    jsComment: '#969896',
    jsFunctionName: '#795da3',
    jsKeyword: '#a71d5d',
    jsPrimitive: '#0086b3',
    jsRegexp: '#183691',
    jsString: '#df5000',
    jsKey: '#555'
});

var accentColor = pen.theme('html').accentColors[Math.random() % pen.theme.accentColors.length];

[Sune Simonsen]

You only need to supply the format if it is not already set on the pen.