Add case data. - Githubissues

For a first draft, the UI can just show circles per region for number of cases.

Tricky bits:

Data is spatially irregular: Not all regions have data, some regions only have data at courser granularity (at the admin1 / state level).
Data is temporally irregular: The case data may be for 1 week, or multiple weeks, and may change. Some regions may only have older data.

There's also no backend support yet (no API endpoint, or even schema). The example data we have is for dengue, and only for 1 state (Bahia).

Main issues:

[x] Add EpiDataStore class, initially just hardcoded w/ fake data.
[x] Extend DataLayer with notion of overlay layers (in addition to existing base layers).
[x] Add controls to OverlayControlsBoxfor toggling overlay layers.
[x] Draw circles in map admin regions, scaled by number of cases. Mouseover popup shows case data details.
[x] Add case data details to SelectedRegionsInfo panel.
[x] Fix EpiDataStore to return data for selected date instead of just the latest data.
[x] Indicate of the time span for the case data in region panel (and maybe also the popup?).

Polish:

[ ] Rename MapColoring, now that it also mediates overlay data layers that aren't just colors.
[ ] The circle marker captures clicks and doesn't select the underlying region. clickable: false disables the mouseover popup :(.
[ ] Consult w/ UX and research on how to display the circle marker:
- [ ] Should it remain the same size on the screen when zooming? Or should zooming in make it bigger?
- [ ] Formula for determining circle size. Currently, using log of cumulative cases over the time span. Also, should it be relative to admin region size?
- [ ] Other styling issues (color, stroke border, opacity, etc.).
[ ] Use nice switch thingy instead of basic toggle button for overlay layers.
[ ] Indicate time span of case data in the time series display. Could even get per-condition history for the region and draw that(!)

unicef / carrotjuice2