Convert system modules to Dependency Injection

When this PR is merged, the profiler will report several errors like "ERROR - Event handler was not attached for event 'get.pending_content' because method 'Zikula\Module\UsersModule\Listener\PendingContentListener::pendingContentListener' is not callable" **this is expected behavior** if (and only if) you are using a development version of the core. Once you reinstall the core or run `upgrade.php` on your original site, this will be take care of. Instead, one can also safely manually delete the `/EventHandler` entries in the `module_vars` table for the **core modules**. if you cannot live with the red errors in your profiler bar.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #1545
| Refs tickets  | -
| License       | MIT
| Doc PR        | -