[WIP] invert inheritance of ModUrl refs #993

This 'inverts' the inheritance of the following classes.

tasks:
- [x] `ZIkula_ModUrl`
- [ ] `Zikula_Hook_AbstractHandler` / `Zikula\Core\Hook\AbstractHookListener`
- [ ] `Zikula_Hook_ValidationProviders` / `Zikula\Core\Hook\ValidationProviders`
- [ ] `Zikula_Hook_ValidationResponse` / `Zikula\Core\Hook\ValidationResponse`