Update on volatility analysis and mini heatmaps

[tonyfujs]

@randrescastaneda @tgherzog Since those were minor changes, I added them directly to Andres's branch. I did the following:

• Applied a consistent theme / color palette
• For heatmaps, I made the color fixed, with a constant of [0, 202] (The maximum # of countries.). Otherwise the heatmaps using data subsets were hard to read.
• Minor updates to the tooltips
• Custom palettes live in utils.R, so it is easy to modify if needed

Will add the new charts on a different branch.

[tgherzog]

@tonyfujs @randrescastaneda I merged both of your PRs but I don't think we're on the same page. The explanation-specific charts that Andres did for section 3 don't have the indicator counts I would expect. For instance, the "no_gap" section shows 4 indicators but I count 12. Explanation A (dropped) shows 9 indicators but I count 15, etc. Note that I'm not using the raw numbers in the database, I'm applying some corrections to business logic, but those corrections result in lower counts for C-G, so that doesn't explain these discrepancies.

The new volatility analysis looks very promising. I'm not quite seeing the high-ranking indicators I would expect, but that could be due to ensuing database updates, so I'll work a bit more on that.