Added media inlining button in settings>labs

refs https://github.com/TryGhost/Toolbox/issues/524

- Having a button in Admin UI allows to manually trigger media inlining job once import has been processed.
- Added a "start" button hidden behind labs calling Admin API endpoint that starts external media inlining job.

ghost/admin/app/controllers/settings/labs.js

@@ -150,6 +150,11 @@ export default class LabsController extends Controller {
         this.utils.downloadFile(this.ghostPaths.url.api(endpoint));
     }
 
+    @action
+    startMediaInlinerAction() {
+        return this.startMediaInliner.perform();
+    }
+
     @action
     confirmDeleteAll() {
         return this.modals.open(DeleteAllModal);
@@ -213,6 +218,19 @@ export default class LabsController extends Controller {
         return RSVP.resolve();
     }
 
+    @(task(function*() {
+        const inlineURL = this.ghostPaths.url.api('db/media/inline');
+        yield this.ajax.post(inlineURL, {
+            dataType: 'json',
+            // @NOTE: the domains list will become input based
+            data: {
+                domains: []
+            }
+        });
+        // TODO: notify user the inliner has started
+    }).drop())
+        startMediaInliner;
+
     @(task(function* (success) {
         this.set('redirectSuccess', success);
         this.set('redirectFailure', !success);

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

@@ -31,6 +31,18 @@
                     </div>
                 </div>
 
+                {{#if this.feature.mediaInliner}}
+                <div class="gh-expandable-block">
+                    <div class="gh-expandable-header">
+                        <div>
+                            <h4 class="gh-expandable-title">Inline external media</h4>
+                            <p class="gh-expandable-description">Download and inline external media files used in posts.</p>
+                        </div>
+                        <button type="button" class="gh-btn" {{on "click" this.startMediaInlinerAction}}><span>Start</span></button>
+                    </div>
+                </div>
+                {{/if}}
+
                 <div class="gh-expandable-block">
                     <div class="gh-expandable-header">
                         <div>