Link together "All users can connect to this connection" and "store password in wallet" and add a configuration option to use system connections by default

When creating a system wide connection, it makes little sense to store the password in the local user's wallet, since that is completely inaccessible by other users. So if a user requests a system connection, update the "store password" option to also store the password system wide and the other way around. Additionally, this introduces an option in the configuration to use system connections by default, which is useful for example on systems using IWD since that doesn't support user-owned connections.