Rewrite parser pipeline

[Azareal]

We're probably going to want a single source of truth rather than supporting numerous formats (Markdown, HTML, and BBCode) in plugins and possibly risk markup showing up when one of these plugins is disabled.

The single source of truth, for instance, could be HTML which the WYSIWYG naturally consumes anyway. Each plugin (or possibly even the core) could take in their respective formats and translate that to HTML.

Translating it back on-demand on the client-side for any BBCode Editors (if there are any) shouldn't be too costly in any case.