Prevent annotation attempts when not signed in

Simply hides the annotation form--which implied you could
use the thing...--and instead tells the user to sign in,
so they can do what they came to do.

h/templates/client/annotation.html

-<header class="annotation-header">
+<header class="annotation-header" ng-if="!vm.annotation.user">
+  <strong>You must be signed in to create annotations.</strong>
+</header>
+
+<div ng-if="vm.annotation.user">
+  <header class="annotation-header">
     <!-- Deletion notice -->
     <span ng-if="!vm.editing && vm.annotation.deleted">Annotation deleted.</span>
 
@@ -35,7 +40,6 @@
       <!-- / Editing controls -->
     </span>
 
-  <span ng-if="!vm.annotation.user">Sign in to save this annotation.</span>
 
     <span class="annotation-collapsed-replies">
       <a class="reply-count small" href=""
@@ -51,10 +55,10 @@
        ng-if="!vm.editing && vm.annotation.updated"
        ng-href="{{vm.baseURI}}a/{{vm.annotation.id}}"
        >{{vm.timestamp}}</a>
-</header>
+  </header>
 
-<!-- Excerpts -->
-<section class="annotation-section"
+  <!-- Excerpts -->
+  <section class="annotation-section"
            ng-repeat="target in vm.annotation.target track by $index">
     <blockquote class="annotation-quote"
                 ng-hide="target.diffHTML && vm.showDiff"
@@ -71,21 +75,21 @@
              ng-model="vm.showDiff"
              ng-click="$event.stopPropagation()"> Show differences</input>
     </div>
-</section>
+  </section>
 
-<!-- / Excerpts -- >
+  <!-- / Excerpts -- >
 
-<!-- Body -->
-<section name="text"
+  <!-- Body -->
+  <section name="text"
            class="annotation-body"
            ng-model="vm.annotation.text"
            ng-readonly="!vm.editing"
            markdown>
-</section>
-<!-- / Body -->
+  </section>
+  <!-- / Body -->
 
-<!-- Tags -->
-<div class="annotation-body form-field" ng-if="vm.editing">
+  <!-- Tags -->
+  <div class="annotation-body form-field" ng-if="vm.editing">
     <tags-input ng-model="vm.annotation.tags"
                 name="tags"
                 class="tags"
@@ -97,19 +101,19 @@
                        min-length="1"
                        max-results-to-show="10"></auto-complete>
     </tags-input>
-</div>
+  </div>
 
-<div class="annotation-section tags tags-read-only"
+  <div class="annotation-section tags tags-read-only"
        ng-if="vm.annotation.tags.length && !vm.editing">
     <ul class="tag-list">
       <li class="tag-item" ng-repeat="tag in vm.annotation.tags">
         <a href="/stream?q=tag:'{{tag.text|urlencode}}'" target="_blank">{{tag.text}}</a>
       </li>
     </ul>
-</div>
-<!-- / Tags -->
+  </div>
+  <!-- / Tags -->
 
-<footer class="annotation-footer">
+  <footer class="annotation-footer">
     <div class="small" ng-if="vm.editing">
       <p ng-show="vm.privacyLevel.text == 'Only Me'">
         <i class="h-icon-lock"></i> This annotation is visible only to you.</p>
@@ -175,4 +179,5 @@
               ng-click="vm.delete()"
               ><i class="h-icon-delete btn-icon"></i> Delete…</button>
     </div>
-</footer>
+  </footer>
+</div>