django CMS 3.0 no longer bundles WYMEditor (or indeed any text editor).
Instead, developers are expected to install their own text editor.
https://github.com/divio/djangocms-text-ckeditor is provided, but not really satisfactory for WYM/Semantic Editor users.
I'm working on a djangocms-text-wymeditor package to provide a WYMEditor for django CMS. Obviously, there can be no Semantic Editor for django CMS until there's a WYMEditor...
I will push my work to GitHub once I have something more or less working.