Add lastseen argument to EOAurl

[kthoden]

Since bibliography entries pointing to a URL can easily contain the date of the last visit by using
Urldate = {2016-02-01} it would be great to have that too in EOAurl command, as well.
Something along the lines of:

\newcommand{\EOAurlnew}[2][\today]{\protect\url{#2} (besucht am #1)}

(besucht am 28. 10. 2015) is how biber formats the Urldate, so they should look similar. One would have to parse the date format, too.