Rename admin users controller/route

Started out as a simple helper page to list LDAP users, but turning into
proper user management now.

app/views/admin/users/index.html.erb

@@ -1,4 +1,4 @@
-<%= render HeaderComponent.new(title: "LDAP Users: #{@ou}") %>
+<%= render HeaderComponent.new(title: "Users: #{@ou}") %>
 
 <%= render MainSimpleComponent.new do %>
   <section>
@@ -22,7 +22,7 @@
       <ul>
         <% @orgs.each do |org| %>
           <li class="inline-block">
-            <%= link_to org[:ou], admin_ldap_users_path(ou: org[:ou]), class: "ks-text-link" %>
+            <%= link_to org[:ou], admin_users_path(ou: org[:ou]), class: "ks-text-link" %>
           </li>
         <% end %>
       </ul>

app/views/shared/_admin_nav.html.erb

@@ -1,7 +1,7 @@
 <%= link_to "Dashboard", admin_root_path,
       class: main_nav_class(@current_section, :dashboard) %>
-<%= link_to "Users", admin_ldap_users_path,
-      class: main_nav_class(@current_section, :ldap_users) %>
+<%= link_to "Users", admin_users_path,
+      class: main_nav_class(@current_section, :users) %>
 <%= link_to "Invitations", admin_invitations_path,
       class: main_nav_class(@current_section, :invitations) %>
 <%= link_to "Donations", admin_donations_path,