[WIP] Focus share link when pop-up opens

Fixes #1673 by waiting for the dropdown to open and then selecting and focusing input.

- [ ] Needs tests.
I think what's happening is that the browser hasn't repainted the element yet and so you can't focus and select it. It's still invisible. A simple $evalAsync seems to be enough to delay it.

Then, for not checking the class in the watcher I suggest we just add a method on the scope. Here's my full solution:

```diff
diff --git a/h/static/scripts/directives/annotation.coffee b/h/static/scripts/directives/annotation.coffee
index 4be4b78..ff4ceb5 100644
--- a/h/static/scripts/directives/annotation.coffee
+++ b/h/static/scripts/directives/annotation.coffee
@@ -306,9 +306,14 @@ annotation = [
           scope.$evalAsync ->
             ctrl.save()
 
-      isShareOpen = -> elem.find('.share-dialog-wrapper').hasClass('open')
-      scope.$watch isShareOpen, (isOpen) ->
-        elem.find('.share-dialog-wrapper input').focus().select() if isOpen
+      shared = false
+      scope.share = (event) ->
+        shared = not shared
+        return unless shared
+        scope.$evalAsync ->
+          angular.element(event.target)
+          .parent().addClass('open')
+          .find('input').focus().select()
 
       # Keep track of edits going on in the thread.
       if counter?
diff --git a/h/templates/client/annotation.html b/h/templates/client/annotation.html
index b0cd056..8139633 100644
--- a/h/templates/client/annotation.html
+++ b/h/templates/client/annotation.html
@@ -116,7 +116,7 @@
     ng-click="vm.reply()"
     ><i class="h-icon-reply"></i> Reply</a>
   <span class="magicontrol share-dialog-wrapper">
-    <a class="small dropdown-toggle" href="" title="Share"
+    <a class="small" href="" title="Share" ng-click="share($event)"
       ><i class="h-icon-export"></i> Share</a>
     <span class="share-dialog" ng-click="$event.stopPropagation()">
       <a class="h-icon-export"
```