Update server url in case of permanent redirection #5972

Update server url in case of permanent redirection #5972

This is the first time the account url may update outside of
account setup.

Summary of redirection handling:
1. During account setup (wizard)
   - status.php gets permanently redirected -> adjust url
   - authed PROPFIND gets *any* redirection -> adjust url
2. During connectivity ping (ConnectionValidator)
   - status.php gets permanently redirected -> adjust url (new!)

All other redirections should be followed transparently and
don't update the account url in the settings.