Add viewer switcher

app/views/projects/blob/_header.html.haml

@@ -12,6 +12,8 @@
       = number_to_human_size(blob.raw_size)
 
   .file-actions.hidden-xs
+    = render 'projects/blob/viewer_switcher', blob: blob unless blame
+
     .btn-group{ role: "group" }<
       = copy_blob_source_button(blob) unless blame
       = open_raw_file_button(namespace_project_raw_path(@project.namespace, @project, @id))

app/views/projects/blob/_viewer_switcher.html.haml

+- if blob.show_viewer_switcher?
+  - simple_viewer = blob.simple_viewer
+  - rich_viewer = blob.rich_viewer
+
+  .btn-group{ role: "group" }
+    - simple_label = "Display #{simple_viewer.switcher_title}"
+    %button.btn.btn-default.btn-sm.js-blob-viewer-switcher.has-tooltip{ 'aria-label' => simple_label, title: simple_label, data: { viewer: 'simple', container: 'body' } }>
+      = icon(simple_viewer.switcher_icon)
+
+    - rich_label = "Display #{rich_viewer.switcher_title}"
+    %button.btn.btn-default.btn-sm.js-blob-viewer-switcher.has-tooltip{ 'aria-label' => rich_label, title: rich_label, data: { viewer: 'rich', container: 'body' } }>
+      = icon(rich_viewer.switcher_icon)