Package Installer Warning Files

[NikRimington]

The ability to include warning files that the backoffice of Umbraco can handle in order to display install and uninstall warnings.

Proposal:

Inclusion of Install.Warnings.md, and Uninstall.Warnings.md in the package format. These are then parsed if present and shown to the user along with a "confirmation of acceptance" type checkbox that they have to acknowledge. This would allow package devs to display install warnings and uninstall warnings to users, for example "uninstalling this package may break your site as it will remove XYX Property Editor".