Updated to-do for 0.6 (Niwi) release

Updated the widget to-do page:
http://wiki.xwt.org/Wiki.jsp?page=WidgetAuditTODO

It's pretty realistic list for 0.6 - it's conceivable that this should 
be completed by me by the time Nitrogen is stable.

I've pushed the text widget stuff back for the 0.7 release simply 
because I don't have the time to learn about the text widget and David 
has been fairly inactive of late.

I've also dropped the theming stuff I mentioned.  Any theme that wants 
to do static things can reference it's own static template.  Any widget 
that wants to use a base theme can preapply that theme's appropriate widget.

I'm going to start going at this quite strongly tomorrow.

- Charlie