Ability to identify custom CSS and HTML customisations and notify the admin of things they need to re-apply or check

Customizations such as Stylesheets (CSS), Custom HTML, and Layouts tend to break post-upgrade, especially to Confluence 5.x (see Upgrade Notes. We need a better way to prevent such upgrade pains on our customers' end, as many of our customers have extensive customizations that they wish to keep post-upgrade. Fixing them manually will only lengthen the upgrade task. (updating variables in layouts, changing CSS classes, etc). Document changes to stylesheets, layouts, JS, and limit their changes between releases, so that it will be less of a struggle.