misc TextEditor changes

This makes three changes to TextEditor:

* implements *setParent*;
* implements *delete*;
* leaves the instance invisible until *setVisible* is called, per the [TextEditor docs](http://developer.nokia.com/resources/library/Java/_zip/GUID-237420DE-CCBE-4A74-A129-572E0708D428/com/nokia/mid/ui/TextEditor.html), which don't say anything about *setParent* triggering a change to visibility.

There's tons more to do to TextEditor, including adding tests. But these are valuable improvements for a midlet I'm testing, especially the *delete* implementation, which is currently blocking important functionality in the midlet.

That's probably true. There are some calculations that should be made relative to the parent, and I wonder if we'll be making them in natives. But if so, we should still be able to access the parent from its Java reference. So I'll make this change.