Umbraco Package Schema and custom-elements at root level

[iOvergaard]

Description

Currently, the files for umbraco-package-schema.json and the custom-elements stuff reside in the "dist-cms" folder. This is due to a legacy thing where only that folder was published and copied over to the CMS. We now support publishing the entire repository to npm and it makes much more sense to put those files, that should be referenced externally at the root level of the package.

Expected behavior

1. umbraco-package-schema.json and other schema files are placed at the root level of the repository/npm package.
2. They are properly ignored with .gitignore
3. They are built with the npm run build:for:npm command