(core) Brings in the new donut charts.

Summary:
  - Donut charts is same as pie chart with few extra options to control size of the hole and to show/hide a big total in it.
  - Add a new option type to tune a numeric options using a slider/spinner/keyboard.
  - Add a new option type to tune a numeric options using a slider/keyboard
  - Add a new .propWithDefault method to ObjObservable to allows to set a default value when options is undefined.
  - mocha-webdriver's findContent does not work to find content in svg elements. So had to tweak original function into a sister function using .textContent instead.

Test Plan: Adds new tests

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: anaisconce, dsagal

Differential Revision: https://phab.getgrist.com/D3107

app/client/lib/chartUtil.ts

@@ -85,3 +85,7 @@ export function consolidateValues(series: Array<{values: Datum[]}>, xvalues: Dat
   }
   return series;
 }
+
+export function formatPercent(val: number) {
+  return Math.floor(val * 100) + " %";
+}