Filter and codex refactoring

Lots of changes! The code from controllers/codex.js has been split up
across multiple, more appropriate files. Additionally, the codex filters
and a dialog for creating new codex entries have also been created (with
their own files).

Everything still seems to be working, too! Note that currently, the
createCodice() method does live server-side, but its isAdmin() method is
returning perma-true for now. Eventually, this should hit against a
server-side list of admin users.

Also, HTML borrowed from the styled example has been incorporated for
individual codices.

The "new codex entry" dialog is fully functioning, and will display
errors on unsuccessful add attempts. However, it doesn't yet provide a
way to add bonuses or restrictions.