Porting an XXE v9 command to XXE v10

The recipe is simple and straightforward:

Extend abstract class CommandBase. Do not implement interface Command. Example:
```
public class WrapElementCmd extends CommandBase {
```
The command must have a constructor which invokes the CommandBase constructor. Example:
```
public WrapElementCmd() {
    super(/*repeatable*/ false, /*recordable*/ true);
}
```

The “execute method” to be implemented is doExecute:

public CommandResult doExecute(DocumentView docView, String parameter,
                               int x, int y) { ... }

The parent component of a dialog box is obtained using DocumentView.getDialogParent. (XXE v9 had DocumentView.getPanel.)
The doExecute method always returns a CommandResult. Therefore
- Replace return EXECUTION_FAILED; by return CommandResult.FAILED; (return CommandResult.CANCELED; after the user clicks Cancel in a dialog box).
- Replace return null; by return CommandResult.DONE;
- Replace return useful_result; by return CommandResult.done(useful_result);
If the command is repeatable, use CommandResult.success to specify how the command is to be repeated. In practice, replace XXE v9 DocumentView.addToCommandHistory:
```
docView.addToCommandHistory(this, "U+" + Integer.toString((char)code, 16), title);
```
by XXE v10 CommandResult.success:
```
CommandResult result =
  CommandResult.success(null, "U+" + Integer.toString((char)code, 16), title);
```
Also make sure to take this pitfall into account.


2. Creating useful add-on descriptors