Merge branch '19003-file-view-subnav' into 'master'

Resolve "Sub nav isn't showing on file view"

## What does this MR do?
Adds subnav to `Repository` > `File` view

## What are the relevant issue numbers?
Closes #19003
Part of #18844

## Screenshots (if relevant)
![Screen_Shot_2016-06-23_at_5.33.05_PM](/uploads/aa6993b2376dbe454af87d852aa74f5e/Screen_Shot_2016-06-23_at_5.33.05_PM.png)

cc @dzaporozhets

See merge request !4890
(cherry picked from commit 2efee5f6)

CHANGELOG

@@ -4,6 +4,7 @@ v 8.9.4
   - Fix privilege escalation issue with OAuth external users.
   - Ensure references to private repos aren't shown to logged-out users.
   - Fixed search field blur not removing focus. !4704
+  - Resolve "Sub nav isn't showing on file view". !4890
 
 v 8.9.3
   - Fix encrypted data backwards compatibility after upgrading attr_encrypted gem. !4963

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

+- @no_container = true
 - page_title @blob.path, @ref
+= render "projects/commits/head"
 
-= render 'projects/last_push'
+%div{ class: (container_class) }
+  = render 'projects/last_push'
 
-%div#tree-holder.tree-holder
+  %div#tree-holder.tree-holder
     = render 'blob', blob: @blob
 
-- if can_edit_blob?(@blob)
+  - if can_edit_blob?(@blob)
     = render 'projects/blob/remove'
 
     - title = "Replace #{@blob.name}"