Fixed bugs with viz in exploreV2 (#1609)

* Fixed bugs with viz in exploreV2

Done:
 - fix typo in pie viz
 - add metrics/groupby to dist_bar viz
 - fix typo in heatmap viz
 - add big_number_total to viz
 - fixed problem with fetching columns for datasource
 - add sqlaTimeSeries to viz
 - change row_limit and limit from number to strings so that we
 don't need to parse integers in bootstrap data

* Fix python tests

* Added order_bars checkbox for dist_bar viz

superset/assets/javascripts/modules/utils.js

@@ -132,14 +132,14 @@ export function formatSelectOptionsForRange(start, end) {
   // returns [[1,1], [2,2], [3,3], [4,4], [5,5]]
   const options = [];
   for (let i = start; i <= end; i++) {
-    options.push([i, i]);
+    options.push([i.toString(), i.toString()]);
   }
   return options;
 }
 
 export function formatSelectOptions(options) {
   return options.map((opt) =>
-     [opt, opt]
+     [opt.toString(), opt.toString()]
   );
 }