Allow stat()ing new-account link.

Summary:
When stat()ing 'gdrive:/new-account', the slave was actually stat()ing the UDS entry for the account root path.
This patch fixes the issue by not having GDriveUrl::isAccountRoot() return true for 'gdrive:/new-account' and also moves the New Account label logic into GDriveUrl.

Reviewers: elvisangelaccio

Reviewed By: elvisangelaccio

Subscribers: KIO GDrive

Tags: KIO GDrive

Differential Revision: https://phabricator.kde.org/D24366