Fix adder from affecting website's height on load

h/static/scripts/annotator/adder.js

@@ -102,9 +102,12 @@ function Adder(container, options) {
     // property rather than `display` so that we can compute its size in order to
     // position it before display.
     display: 'block',
-    position: 'absolute',
     visibility: 'hidden',
 
+    // take position out of flow and off screen initially
+    position: 'absolute',
+    top: 0,
+
     // Assign a high Z-index so that the adder shows above any content on the
     // page
     zIndex: 999,