add nzo.nzo_id to user script params

_Replaces #90, now based off sabnzbd/develop_

Pass the `nzo.nzo_id` to [post processing scripts](http://wiki.sabnzbd.org/user-scripts) as the last parameter to maintain compatibility.

API uses `nzo.nzo_id` as primary and not being able to easily reference this in post processing scripts is inflexible.

[Suggested addition to docs](http://wiki.sabnzbd.org/user-scripts):

```
|| 8 || Job ID e.g. SABnzbd_nzo_wgmb1m ||
```