Fix password recovery URL

The confirmation link that gets sent to users during password recovery is not recognised as valid link by Frogsystem 2, if the website uses the default URL style.
This is caused by the URL function (which already delivers HTML encoded URLs, i.e. "&" is replaced by "&amp;") and the HTML mail, which seems to encode the URL again, causing invalid HTML URLs like http://www.example-frogsystem-2-site.com/?confirm&amp;amp;h=foobar instead of http://www.example-frogsystem-2-site.com/?confirm&amp;h=foobar in the confirmation mail.

This pull request fixes the issue by replacing "&amp;" with "&" in the confirmation URL. It also adds some missing language texts that appear, if the hash is invalid.