Facilitate enable/disable of Deputy Systems on module installation/disablement.

Since Deputy cannot be told to react to random module installations, there's nothing that can be done to be sure any systems defined by a given hook_deputy_default_systems() invocation are probably turned on or off along with the implementing module's status changes. However, a bit of documentation might guide developers to do something like:

/**
 * Implementation of hook_install().
 */
function example_install() {
  module_load_include('module', 'deputy');
  deputy_activate_default_systems('example');
}

/**
 * Implementation of hook_disable().
 */
function example_disable() {
  module_load_include('module', 'deputy');
  deputy_deactivate_systems('example');
}

/**
 * Implementation of hook_uninstall().
 */
function example_uninstall() {
  module_load_include('module', 'deputy');
  deputy_uninstall_systems('example');
}