Add hotspot enhancements and improed styles

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

modules/glmv.js

@@ -160,6 +160,17 @@ slideshowAnnotations = function(mView, slideDuration = 5000) {
     }
 }
 
+/**
+ * Toggle visibility of all annotations
+ * 
+ * @param {ModelViewer} mView 
+ */
+toggleAnnotations = function(mView) {
+    [...mView.querySelectorAll('button')].forEach( hs => {
+        hs.toggleAttribute('hidden')
+    })
+}
+
 /**
  * Prepare to drag a hotspot
  *