Add migration to convert all Node uriPathSegment to lowercase

[t-heuser]

At the moment in the README it says:
Note: The lowercase redirect is deactivated by default, because you have to make sure, that there is no uriPathSegment with camelCase or upperspace letters - this would lead to redirects in the neverland.

We can remove that note and activate lowercase redirects per default if we add an migration that converst all Node uriPathSegment to lowercase.

We can use the migration from here: https://github.com/visol/Visol.Neos.CaseInsensitiveUrls