added plugin band.py

band.py polls last.fm for information about an artist.
see below example

<@banjax> .band speedwolf
<gaahl> (banjax) Speedwolf has 4279 listeners. Tags: thrash metal, speed metal, metal punk, metal, heavy metal. Similar artists: Chapel, Deathhammer, Syphilitic Vaginas, Trench Hell, Ketzer. More info on http://www.last.fm/music/Speedwolf