largefiles: make cloning not ask two times about password (issue4883) Before this commit url.opener overwritten stored password for connection with given url/user even when new password for given connection was not filled. This commit makes opener overwrites saved authentication only when it contains password.

url: remember http password database in ui object This makes http password database stored in ui object. It allows reusing authentication information when we use this database for creating password manager for the new connection.