Provide a method for retrieving the content type slug
Add a class to handle core meta data for our content types
Introduce `get_object_type_slugs()` to reduce repetition of sameness

We need a public facing method so that we can better retrieve the
list of content type slugs on the outside. While doing this, there's
a benefit for using it internally as well.
We're only using one parameter in the add_meta_boxes action
s/project/people/ when gathering content type slugs
Add a meta box to capture a URL for all object types
Update CHANGELOG
Merge pull request #10 from washingtonstateuniversity/capture-urls

[PR] Add a meta box to capture a URL for all object types