* Fix offline upgrade download link
In Firefox (92.0.1) `href="#"` does not allow to start downloading of `upgrade.html` (Chrome has no such problem). Making href completely empty fixes the issue.
* Update plugins/tiddlywiki/upgrade/UpgradeWizard.tid
Importing an encrypted wiki ordinarily doesn’t place the password in
the password vault on the basis that one ought to be able to import
from a file without automatically inheriting its password.
Now there’s a configuration option that can be used by the upgrade
plugin to cause the password vault to be updated with any password
entered by the user. The end result is that the user only needs to
enter their password once.
