Improve some Text Editor editor settings

[MewPurPur]

Some improvements and fixes to outdated information. Hardly any of these tweaks are relevant to 3.x, so no 🍒-picking.

The show_bookmark_gutter setting... maybe we should remove it or rename to "show_bookmarks_in_gutter"? Seems quite pointless, also, from a user's perspective, bookmarks don't have their own gutter, they share one with breakpoints and executing lines.