Revert "Diameter preference is unused."

This reverts commit 55cc20ec96.

client/lib/settings.js

@@ -10,11 +10,21 @@ window.settings = {
   'staticmaps_key': 'AIzaSyDtGhiAnSdg9TaGZC_daNcQe43BS8Ws7Iw'
 };
 
+window.c = function () {
+  return Math.PI * localStorage.diameter * 2.54 / 100;
+};
+
+if (_.has(localStorage, 'diameter') && !_.isNumber(localStorage.diameter)) {
+  delete localStorage.diameter;
+}
+
+
 if (_.has(localStorage, 'multiplier') && !_.isNumber(localStorage.multiplier)) {
   delete localStorage.multiplier;
 }
 
 _.defaults(localStorage, {
+  diameter: 28,
   multiplier: 2.5
 });