Add Admin UI

app/controllers/admin/conferences_controller.rb

app/controllers/admin/roles_controller.rb

app/helpers/admin/roles_helper.rb

app/views/admin/conferences/edit.html.erb

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

app/views/admin/conferences/new.html.erb

app/views/admin/roles/edit.html.erb

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

app/views/admin/roles/update.html.erb

config/routes.rb

lib/tasks/admin.rake

lib/tasks/events_admin.rake

test/controllers/admin/roles_controller_test.rb