$allowed_actions for GridField subclass
$allowed_actions for GridField subclass

Taken from https://github.com/silverstripe/silverstripe-subsites/pull/94,
thanks @frankmullenger

danaenz/silverstripe-subsites,mikenz/silverstripe-simplesubsites,dnadesign/silverstripe-subsites,silverstripe/silverstripe-subsites,mandrew/silverstripe-subsites,silverstripe/silverstripe-subsites,wernerkrauss/silverstripe-subsites,danaenz/silverstripe-subsites,mikenz/silverstripe-simplesubsites,wernerkrauss/silverstripe-subsites,dnadesign/silverstripe-subsites,mandrew/silverstripe-subsites