Remove WordPress as a submodule

It seems to make more sense that verified updates to WordPress core
are committed to the platform rather than implemented as a submodule.

While we'd like to avoid running patched WordPress core code in
production, it's always possible that we test something to resolve
an issue that can then be fixed officially.

We'll have to determine the proper system for maintaining this version
of WordPress. Likely most updates will just be rsynced from the core
git repository.
Introduce WordPress core as of core git commit 4a9eee5
Remove Twenty Ten theme from our installation
Remove Twenty Eleven from our installation
Remove Twenty Thirteen from our installation
Remove the entire wp-content/themes directory

We'll be providing themes in completely different wp-content directory.
There really isn't a need to track changes here. We can sync any default
themes that we want separately.
Remove entire wp-content/plugins directory

We'll leave wp-content just in case. :)
Merge pull request #53 from washingtonstateuniversity/wp-nonsub

[PR] Stop tracking WordPress as a submodule