cmd/bosun: Add normalize switch to graph page to display series on 0-…

…100 scale

Each series is displayed on a scale of 0-100. This helps to visually see if there is apparent correlation between metrics with vastly different scales. I tried to other options, d3.power scales and d3.log scales. Power scales weere not effective for getting good correlation views. Log scales don't implement well for ad-hoc graphing. There can't be 0 values, series cannot cross the positive/negative threshold, and negative series must be handled differently.