Fix share dialog

Previously, the event from the initial click on the "share" event was
swallowed by the click handler on the parent thread:

    https://github.com/hypothesis/h/blob/fef9f43/h/static/scripts/directives/thread.coffee#L198-L221

Removing this has meant that the share dialog never shows.

Incidentally, this also fixes #1802, which was caused by the same code
in the thread directive, which swallowed all click events from its
children and hence prevented the closure of the share dialog.

h/static/scripts/directives/annotation.coffee

@@ -314,10 +314,15 @@ annotationDirective = [
             ctrl.save()
 
       scope.share = (event) ->
-        scope.$evalAsync ->
         $container = angular.element(event.target).parent()
         $container.addClass('open').find('input').focus().select()
+
+        # We have to stop propagation here otherwise this click event will
+        # re-close the share dialog immediately.
+        event.stopPropagation()
+
         $document.one('click', (event) -> $container.removeClass('open'))
+        return
 
       # Keep track of edits going on in the thread.
       if counter?