Added saved post status indicator behind labs flag

refs https://github.com/TryGhost/Team/issues/779

- add "- Saved" to status text in editor when a post has no unsaved changes
- uses `savedIndicator` labs flag so we can test and tweak behaviour before go-live

ghost/admin/app/components/gh-editor-post-status.hbs

@@ -8,6 +8,7 @@
         {{else if (eq @post.email.status "submitted")}}
             and sent to {{gh-pluralize @post.email.emailCount "member"}}
         {{/if}}
+        {{if (not @hasDirtyAttributes) "- Saved"}}
     {{else if @post.isScheduled}}
         <time datetime="{{@post.publishedAtUTC}}" class="ml1 green f8" data-test-schedule-countdown>
             Will be published
@@ -16,9 +17,10 @@
             {{/if}}
             {{this.scheduledTime}}
         </time>
+        {{if (not @hasDirtyAttributes) "- Saved"}}
     {{else if @post.isNew}}
         New
     {{else}}
-        Draft
+        Draft {{if (not @hasDirtyAttributes) "- Saved"}}
     {{/if}}
 </div>

ghost/admin/app/services/feature.js

@@ -56,6 +56,7 @@ export default Service.extend({
     matchHelper: feature('matchHelper'),
     multipleProducts: feature('multipleProducts', {developer: true}),
     emailCardSegments: feature('emailCardSegments', {developer: true}),
+    savedIndicator: feature('savedIndicator', {developer: true}),
 
     _user: null,
 

ghost/admin/app/templates/editor.hbs

@@ -21,6 +21,7 @@
                         <span>
                             <GhEditorPostStatus
                                 @post={{this.post}}
+                                @hasDirtyAttributes={{this.hasDirtyAttributes}}
                                 @isSaving={{or this.autosaveTask.isRunning this.saveTasks.isRunning}}
                             />
                         </span>

ghost/admin/app/templates/settings/labs.hbs

@@ -280,6 +280,19 @@
                         </div>
                     </div>
                 </div>
+                <div class="gh-expandable-block">
+                    <div class="gh-expandable-header">
+                        <div>
+                            <h4 class="gh-expandable-title">Show saved state in editor</h4>
+                            <p class="gh-expandable-description">
+                                Post status in editor shows "- Saved" when a post has no unsaved changes
+                            </p>
+                        </div>
+                        <div class="for-switch">
+                           <GhFeatureFlag @flag="savedIndicator" />
+                        </div>
+                    </div>
+                </div>
             </div>
         </div>
         {{/if}}