Add fullscreen framework

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

modules/glmv.js

@@ -413,4 +413,17 @@ downloadImage = function(defName) {
         .then(imgBlob => {
             reader.readAsDataURL(imgBlob)
         })
+}
+
+/**
+ * Respond to full screen changes on the gl container
+ * 
+ * @param {Element} glCont container element to enlarge or reduce
+ */
+toggleFullScreen = function(glCont) {
+    if (document.fullscreenElement) {
+        document.exitFullscreen()
+    } else {
+        glCont.requestFullscreen()
+    }
 }