Nitrogen Widgets - Niwi

Niwi, the new code name for the Nitrogen Widgets.

For Niwi I'd like to move away from the old method of instantiating 
themes, as I have previously mentioned.

So...

<static>
     xwt.theme( "xwt.theme", "path.to.theme" );
</static>

Becomes...

<preapply name="xwt.widget.frame" />
<template theme="path.to.theme" />

This allows for XWT to change the way theming occurs without application 
developers having to know about it, presuming they use an up-to-date 
widget set.

It also gives a nice starting point from which we can create some useful 
static variables.

Forever may we be known as the Knights of Niwi.  Niwi!  Niwi!  (Even 
more annoying than Ni!!!)

My priorities (in order of importance) are the following:
- Table
- Tree
- Port the rest to Nitrogen

A lot of porting will be required regardless (due to the depracation of 
several nitrogen features).

I'm also going to create 2 extra subthemes; basicimage and basicsvg, 
which will hold basic implementations of certain image-based and 
svg-based widgets for image-based and svg-based themes respectively. 
This will be a place-holder for things like borderable.  (An svg border 
would be done differently to an image border.)

- Charlie