XML Element Wrapper enhancements (keep, etc)

- [x] Support lazy instantiation of collection lists in 'replaced' code
- [x] Support deleting unused collection-classes
- [ ] Support keeping certain classes when deleting unused collection-classes is enabled (aka 'control' file list of classes and behavior

Sample config from other xew plugins (ref: https://github.com/dmak/jaxb-xew-plugin):
```
-Xxew
-Xxew:control items-schema.xew
-Xxew:instantiate lazy
-Xxew:collection java.util.LinkedList
```

Schema snippet:

```

```

Creates:
```
com.company.Items;
com.company.Item;
```

1. When 'control' is enabled, the Items class is deleted
2. When control file has 'com.company.Items=keep' listed, the class is _not_ deleted