feat(imageLoader):Add an nth image loader strategy (#10) (#3044)

* feat(imageLoader):Add an nth image loader strategy (#10)

* Updates for PR for nth menu

* performance:Prior implementation was O(n^2), taking about 50 ms

* feat:Nth image loader, added docs as requested

extensions/cornerstone/src/getHangingProtocolModule.ts

@@ -8,6 +8,7 @@ const mpr = {
   availableTo: {},
   editableBy: {},
   protocolMatchingRules: [],
+  imageLoadStrategy: 'nth',
   displaySetSelectors: {
     mprDisplaySet: {
       seriesMatchingRules: [