Split viewer code into trackview.js

Also disabled iOS hack, as it seems to be causing issues, and fixed a
minor drag-n-drop bug (wouldn't load if track was already playing past
length of newly loaded track).

To play without a viewer, you still have to stub it out. Not sure the
best way to handle that case yet.

index.html

@@ -2,6 +2,7 @@
   <title>js xm</title>
   <script src="http://a1k0n-pub.s3-website-us-west-1.amazonaws.com/xm/xmlist.js"></script>
   <script src="xmeffects.js"></script>
+  <script src="trackview.js"></script>
   <script src="xm.js"></script>
   <style>