Dashboard charts: Add legend or description of score buckets

[ecumike]

Without a point of reference, a user might not understand the donut scores are out of 100.
As well, the pie charts with poor/avg/good have no reference as to what score is actually "good".
And the third set, the timing charts, same thing.. what "time" is good/avg/poor?

Need a way to visually tell the user (like a legend) a reference point for the sets of charts.

Most likely, this should be combined with #69 and solved using that new data model. Google buckets are already set as global vars.