access plugins allow context based access control to pages.
'title' => Title of the plugin
'description' => Description of the plugin
'callback' => callback to see if there is access is available. params: $conf, $contexts, $account
'required context' => zero or more required contexts for this access plugin
'default' => an array of defaults or a callback giving defaults
'settings form' => settings form. params: &$form, &$form_state, $conf
settings form validate
settings form submit
warning: Your settings array will be stored IN THE MENU SYSTEM to reduce loads, so be TRIM.