fix markup to handle tags as an unordered list of links

It also moves the styling of tags as "foo, bar." (note: comma and dot)
from the javascript code into the CSS so that it becomes easier
to tweak it to anybodys personal liking without needing to change code
make the back-button work by working with onhashchange

Reacting on click events on the tags has the disadvantage of
preventing the back/forward button of a browser to work, so
this code reacts to the (relatively new) hashchange events.

It's not perfect, as it is not supported by (old) browsers and
doesn't support 'untagged' in the same way, but good enough for me
support favicon display by using a pre-built collection

Add support to load favicons from a common URI based on the
hostname of the bookmark as it is nearly impossible to guess the
favicon of the bookmark correctly.

As an example the DuckDuckGo collection can be used, but it is
a small one and a bit unfair to us their bandwidth (beside that
requesting a bunch of small files from remote isn't exactly fast, too)
So you really want to roll your own collection if you want to use
this feature. Otherwise just leave it disabled, which is the default.