Fix PermissionKey::add() declaration
Fix PermissionKey::add() declaration

- Add `static` declaration to `PermissionKey::add()`

MichaelMaar/concrete5,matt9mg/concrete5,TimDix/concrete5,TimDix/concrete5,matt9mg/concrete5,MichaelMaar/concrete5,matt9mg/concrete5,avdevs/concrete5,TimDix/concrete5,avdevs/concrete5,MichaelMaar/concrete5,avdevs/concrete5