Incorrect Heatmap Bucketing

[rsandor]

The _prepareEntry method of Epoch.Time.Heatmap is responsible for transforming a sparse histogram into the correct number of buckets (buckets option) given a range (bucketRange option). The way we currently do this is pretty lazy and generally considered to be "jank" (technical term). This can have some very weird effects on the graphical output of the plot, here's an example:

This should be a plot of a normal distribution stretched over the range [0, 100) across 45 buckets. Clearly there are some weird numerical errors cropping up due to the so-called "jankness" of our bucketing routine.

Here's what needs to be done:

• Create a test in the tests/real-time/heatmap.html that reproduces the beahvior
• Implement a better _prepareEntry method that does not suffer from this problem