Modify gas price statistics (#2947)

* gas price distribution + median + tests

* put histogram in util

* use the util histogram

* remove the default gas price implementation

* histogram rpc

* fix empty corpus

* Add JS ethcore_gasPriceHistogram

* Fix typo (s/types/type/) & subsequent failing test

* Fix return type & formatting

* bucketBounds

* Add jsapi e2e test verification

js/src/api/format/output.js

@@ -70,6 +70,20 @@ export function outDate (date) {
   return new Date(outNumber(date).toNumber() * 1000);
 }
 
+export function outHistogram (histogram) {
+  if (histogram) {
+    Object.keys(histogram).forEach((key) => {
+      switch (key) {
+        case 'bucketBounds':
+        case 'counts':
+          histogram[key] = histogram[key].map(outNumber);
+      }
+    });
+  }
+
+  return histogram;
+}
+
 export function outLog (log) {
   Object.keys(log).forEach((key) => {
     switch (key) {