Style RFC: Avoiding use of default namespace

Most of the code in the niwi module has lines like:

<xwt xmlns="xwt.theme" xmlns:lib="...">

The above line sets the default namespace to xwt.theme. I would like to 
suggest we avoid this, for three reasons:

1) It sets a bad example for user applications, where
    it will cause havoc. Eg, org/xwt/sampler/main.xwt:

       <xwt xmlns="xwt.widget">
           <template>
               <box fill=".org.xwt.sampler.test" />
           </template>
       </xwt>

    The above fails, as the core attaches the default
    uri for an image lookup and tries to find:

    ./xwt/widget/org/xwt/sampler/test[.png/.jpg/.gif]

2) XWT almost makes complete use of the Namespacing
    spec, with one exception. The XWT tags themselves
    should be defined by a Namespace (<xwt>, <box>,
    <template>). If these tags are defined by a
    Namespace, then they should be the default uri.

    This is already the situation from a practical
    perspective, I just want to formalise it by saying
    it shouldn't be possible to redefine the default
    Namespace.

3) Prefix standardisation. If we use prefixes for all
    template access, then we can have a set of prefixes
    that remain the same across the widget library, and
    we can recommend for use in user applications.

      widget - xwt.widget
      theme  - xwt.theme
      lib    - xwt.lib
      ... etc

    At the moment, sometimes we have xmlns="xwt.widget",
    and other times xmlns="xwt.theme". This means copy
    and pasting an xml block from one file to another
    will change the behaviour of the xml.


Thoughts?

d