Added ability to use timeseries and intervals for y axis

Added ability to use a times series for the y axis and set the interval like so.

    var args = {
        data: {
            columns: [
                ["times", 60000, 120000, 180000, 240000]
            ]
        },
        axis: {
            y: {
                type : 'timeseries',
                ticks : {
                    time : {
                        value : 'seconds',
                        interval : 30
                    }
                },
            },
        }
    };
You can specify any time value that corresponds with D3 https://github.com/mbostock/d3/wiki/Time-Intervals