Remove unused APIs and tests (fixes #1)

In this branch I've removed all the unused APIs and tests, leaving just enough to run the `build-news` tool and the `NewsBuilderTests`.

I renamed the main package directory to `newsbuilder` so that it doesn't clash with those `twisted` components which are still required. 

That makes the changeset a bit bit difficult to review, but if you look at the commit log, you can see the diff where I do the removals https://github.com/twisted/newsbuilder/commit/90f478ed6acf40bca6cfc7d58360d66a63e39aa8

If you check out this branch and have twisted installed, you should be able to run eg:

`$ PYTHONPATH=$(pwd) ./bin/admin/build-news /home/richard/projects/Twisted/trunk`

AND

`trial newsbuilder`

Fixes: #1