Idea: pmpro_getAllLevels should include "all" get_pmpro_membership_level_meta

[zagarskas]

When pmpro_getAllLevels() is called https://github.com/strangerstudios/paid-memberships-pro/blob/2d0acf70f615d3e72a4e1154ddc2492cac609785/includes/functions.php#L2262

it should include all custom meta that has been added to any level via get_pmpro_membership_level_meta() Consider how this solution works for grabbing ALL user meta: $allmeta = array_map( function( $a ){ return $a[0]; }, get_user_meta( $user_id ) );

For example

// running this
update_pmpro_membership_level_meta( 1, "custom_meta_key", "my value");	

// does not cause this to happen when pmpro_getAllLevels() is called
 stdClass Object(
    [id] => 1
    [name] => Cool Membership
    ...ect...
    [custom_meta_key] => my value
)

which means this does not work

$pmpro_all_levels = pmpro_getAllLevels(false, true);
 foreach($pmpro_all_levels as $level) {
      echo $level->custom_meta_key;  // convenient, but not work
  }

which means this has to be done

$pmpro_all_levels = pmpro_getAllLevels(false, true);
 foreach($pmpro_all_levels as $level) {
    // we must instead run this
    $meta = get_pmpro_membership_level_meta($level->id, "custom_meta_key", true);   // notconvenient
  }