dataprovider: add naming rules

naming rules allow to support case insensitive usernames, trim trailing
and leading white spaces, and accept any valid UTF-8 characters in
usernames.

If you were enabling `skip_natural_keys_validation` now you need to
set `naming_rules` to `1`

Fixes #687

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

httpd/api_folder.go

@@ -58,6 +58,7 @@ func updateFolder(w http.ResponseWriter, r *http.Request) {
 	}
 	users := folder.Users
 	folderID := folder.ID
+	name = folder.Name
 	currentS3AccessSecret := folder.FsConfig.S3Config.AccessSecret
 	currentAzAccountKey := folder.FsConfig.AzBlobConfig.AccountKey
 	currentAzSASUrl := folder.FsConfig.AzBlobConfig.SASURL