api keys: rework API key UI.

* Add an explanation of what an API key is and how to use it.
* Make it possible for the site owner to view all API keys.
* Remove the requirement to re-enter your password before you can view
  your API key (to be reworked).
* Move the API key controller from maintenance/user/api_keys_controller.rb
  to a top level controller.

config/routes.rb

@@ -53,12 +53,11 @@ Rails.application.routes.draw do
       resource :count_fixes, only: [:new, :create]
       resource :email_notification, :only => [:show, :destroy]
       resource :deletion, :only => [:show, :destroy]
-      resource :api_key, :only => [:show, :view, :update, :destroy] do
-        post :view
-      end
     end
   end
 
+  resources :api_keys, only: [:create, :index, :destroy]
+
   resources :artists do
     member do
       put :revert
@@ -247,9 +246,7 @@ Rails.application.routes.draw do
       post :send_confirmation
     end
     resource :password, only: [:edit, :update]
-    resource :api_key, :only => [:show, :view, :update, :destroy], :controller => "maintenance/user/api_keys" do
-      post :view
-    end
+    resources :api_keys, only: [:create, :index, :destroy]
 
     collection do
       get :custom_style