Set code blocks to full width

[dvz]

Code blocks currently have variable width and may overflow: https://docs.mybb.com/1.8/administration/security/https/

[justinsoltesz]

Code blocks now have a maximum width and will break lines if necessary. I've pushed commits to the mybb.com and docs.mybb.com repositories so they will update.

[dvz]

Code block content should now wrap instead of overflowing in .wrapper, and should wrap in relation to the table of contents (which was problematic on pages like https://docs.mybb.com/1.8/development/plugins/database-methods/) once the cached CSS expires. pre elements are still rendered under .toc though (resulting in the gray background being cut), so it might be better if e.g. the listing is hidden by default or takes 100% width on top so we don't have to deal with float side effects.