Fix confusing behaviour of back link in CI sidebar

Back link should always be responsible for sidebar navigation below.
It should change sidebar navigation to one level up

app/views/layouts/ci/_nav_build.html.haml

-= render 'layouts/ci/nav_project',
-    back_title: 'Back to project commit',
-    back_url: ci_project_ref_commits_path(@project, @commit.ref, @commit.sha)

app/views/layouts/ci/_nav_commit.haml

-= render 'layouts/ci/nav_project',
-    back_title: 'Back to project commits',
-    back_url: ci_project_path(@project)

app/views/layouts/ci/_nav_project.html.haml

 %ul.nav.nav-sidebar
   = nav_link do
-    = link_to defined?(back_url) ? back_url : ci_root_path, title: defined?(back_title) ? back_title : 'Back to Dashboard', data: {placement: 'right'}, class: 'back-link' do
+    = link_to ci_root_path, title: 'Back to CI projects', data: {placement: 'right'}, class: 'back-link' do
       = icon('caret-square-o-left fw')
-      %span= defined?(back_title) ? back_title : 'Back to Dashboard'
+      %span= 'Back to CI projects'
   %li.separate-item
   = nav_link path: ['projects#show', 'commits#show', 'builds#show'] do
     = link_to ci_project_path(@project) do

app/views/layouts/ci/build.html.haml

@@ -8,4 +8,4 @@
     - else
       = render "layouts/header/public", title: header_title
 
-    = render 'layouts/ci/page', sidebar: 'nav_build'
+    = render 'layouts/ci/page', sidebar: 'nav_project'

app/views/layouts/ci/commit.html.haml

@@ -8,4 +8,4 @@
     - else
       = render "layouts/header/public", title: header_title
 
-    = render 'layouts/ci/page', sidebar: 'nav_commit'
+    = render 'layouts/ci/page', sidebar: 'nav_project'