Added hotkey support to viewerbase

Packages/viewerbase/lib/switchToImageRelative.js

@@ -0,0 +1,13 @@
+/**
+ * This function switches to an image given an element and 
+ * the relative distance from the current image in the stack
+ * 
+ *      e.g. switchToImageRelative(element, -1) to switch to currentImageIdIndex - 1
+ * 
+ * @param element
+ * @param {number} [distanceFromCurrentIndex] The image index in the stack to switch to.
+ */
+switchToImageRelative = function(distanceFromCurrentIndex) {
+    var element = getActiveViewportElement();
+    cornerstoneTools.scroll(element, distanceFromCurrentIndex);
+};