added BTS header navigation partial, converted to .slim

app/views/layouts/_header_navigation.html.slim

@@ -0,0 +1,24 @@
+nav.navbar.navbar-default
+  .container-fluid
+    .navbar-header
+      button.navbar-toggle.collapsed type='button' data-toggle='collapse' data-target='#navbar' aria-expanded='false' aria-controls='navbar'
+        span.sr-only Toggle navigation
+        span.icon-bar
+        span.icon-bar
+        span.icon-bar
+      = link_to 'Rails 5 Group Chat', root_path, class: 'navbar-brand'
+
+    #navbar.collapse.navbar-collapse
+      ul.nav.navbar-nav.navbar-right
+        - if user_signed_in?
+          li.dropdown
+            = link_to '/', class: 'dropdown-toggle', :'data-toggle' => 'dropdown', :'role' => 'button', :'aria-haspopup' => 'true', :'aria-expanded' => 'false' do
+              = current_user.username 
+              span.caret
+            ul.dropdown-menu
+              li = link_to 'Settings', edit_user_registration_path
+              li.divider role='separator'
+              li = link_to 'Logout', destroy_user_session_path, method: :delete
+        - else
+          li = link_to 'Sign Up', new_user_registration_path
+          li = link_to 'Login', new_user_session_path