[bukuserver] URIs of xmpp: mailto: etc.

Let user add `tel:`, `magnet:`, `mailto:`, `ssh:`, `irc://`, `git://` URIs.
bukuserver says "Invalid URL."

~~On another note...~~
~~There are plenty of uses to bookmarks, not just `ftp`/`http` links.~~
~~I once wanted to put my contact list into bookmarks but the web browser I was using didn't allow doing so, so I resorted to a directory with 3K of `.vcf` files.~~