Add internalization to admin > projects page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/admin/projects/index.html.haml

-- page_title "Projects"
+- page_title _('Projects')
 - params[:visibility_level] ||= []
 
 .top-area.scrolling-tabs-container.inner-page-scroll-tabs
   %ul.nav-links.nav.nav-tabs
     - opts = params[:visibility_level].present? ? {} : { page: admin_projects_path }
     = nav_link(opts) do
-      = link_to admin_projects_path do
-        All
+      = link_to _('All'), admin_projects_path
 
     = nav_link(html_options: { class: active_when(params[:visibility_level] == Gitlab::VisibilityLevel::PRIVATE.to_s) }) do
-      = link_to admin_projects_path(visibility_level: Gitlab::VisibilityLevel::PRIVATE) do
-        Private
+      = link_to _('Private'), admin_projects_path(visibility_level: Gitlab::VisibilityLevel::PRIVATE)
     = nav_link(html_options: { class: active_when(params[:visibility_level] == Gitlab::VisibilityLevel::INTERNAL.to_s) }) do
-      = link_to admin_projects_path(visibility_level: Gitlab::VisibilityLevel::INTERNAL) do
-        Internal
+      = link_to _('Internal'), admin_projects_path(visibility_level: Gitlab::VisibilityLevel::INTERNAL)
     = nav_link(html_options: { class: active_when(params[:visibility_level] == Gitlab::VisibilityLevel::PUBLIC.to_s) }) do
-      = link_to admin_projects_path(visibility_level: Gitlab::VisibilityLevel::PUBLIC) do
-        Public
+      = link_to _('Public'), admin_projects_path(visibility_level: Gitlab::VisibilityLevel::PUBLIC)
 
   .nav-controls
     .search-holder