htmlparser: Fetch mboxes from FTP servers

FTP servers return a plain page that contains the list
of files on the directory. Each line has the next pattern

  -rw-r--r--  1  500  500  1799055  Sep 30  2013  mbox

where 'mbox' is the file name. This commit adds the code for
parsing those lines.

Fixes issue #33
htmlparser: Use urlparse to get URL scheme
htmlparser: Fix error sorting MBox links

Using sort() method caused that MBox files with format '%Y-%B'
(i.e 2014-May) were not analyzed from oldest to newest.
In Mailman, files (or links) are list from newest to oldest so
we needed to invert the order.