Move header to Epics index page

ee/app/views/shared/_epics.html.haml

-.top-area
-  = render 'shared/issuable/epic_nav', type: :epics
-  .nav-controls
-    - if can?(current_user, :create_epic, @group)
-      - content_for :page_specific_javascripts do
-        = webpack_bundle_tag 'common_vue'
-        = webpack_bundle_tag 'new_epic'
-      #new-epic-app{ data: { endpoint: request.url, 'align-right' => true } }
-
 %ul.content-list.issuable-list
   = render partial: 'groups/epics/epic', collection: @epics