Build Levels page now has links to the pages listing all levels.

Build Levels page now has links to the pages listing all artist & non-artist levels, just for convenience.
oh, and if you didn't know about rake routes:
````
> ./bin/rake routes | grep game_level                                                                          
             game_level_edit_blocks GET      /games/:game_id/levels/:level_id/edit_blocks/:type(.:format)   levels#edit_blocks
           game_level_update_blocks POST     /games/:game_id/levels/:level_id/update_blocks/:type(.:format) levels#update_blocks
                   game_level_clone POST     /games/:game_id/levels/:level_id/clone(.:format)               levels#clone
                        game_levels GET      /games/:game_id/levels(.:format)                               levels#index
                     new_game_level GET      /games/:game_id/levels/new(.:format)                           levels#new
                    edit_game_level GET      /games/:game_id/levels/:id/edit(.:format)                      levels#edit
                         game_level GET      /games/:game_id/levels/:id(.:format)                           levels#show
````