Add hotpot navigation and slideshow

Signed-off-by: Justin Georgi <justin.georgi@gmail.com>

modules/glmv.js

@@ -1,3 +1,5 @@
+let slideShowInterval = null
+
 /**
  * Sets listener and attributes on model-viewer to
  * allow for click registering of a new hotspot
@@ -151,5 +153,10 @@ prevAnnotation = function(mView) {
  * @return {intervalID} ID of the created interval timer
  */
 slideshowAnnotations = function(mView, slideDuration = 5000) {
-    return setInterval(nextAnnotation, slideDuration, mView)
+    if (slideShowInterval) {
+        clearInterval(slideShowInterval)
+    } else {
+        nextAnnotation(mView)
+        slideShowInterval = setInterval(nextAnnotation, slideDuration, mView)
+    }
 }