[Feature proposal] Grid of change presence

### Problem
1. When zoomed out, I don't know where changes are in the current time view
2. When zoomed out, I don't know where changes are in the entire time range of potential changes

### Solution
P1. Generate a heatmap grid of changes in the current time view when zoomed out. Similar to clustering, but could potentially allow for a more normalized area visualization. Provide a single-axis color map for the heatmap to indicate less > more change
P2. Generate a multivariate grid visualization to indicate change over a set time range when zoomed out. Answers both the question "where was the most change?" as well as "_when_ was the most change?"