Gives names to structs that get typedef'd

I don't know if this improves compatibility, but it makes them look
nicer in QtCreator's Outline view.
Removes JavaClass#getclassname()

This will be accessible as getName() someday, hopefully.
Removes JavaClass#getfield()

We won't need wrappers for fields anymore.
Removes JavaField

The logic in convert has been kept but will probably need to change
quite a lot.