Fix non-unique report_ids

This PR is for tracking implementation of the first phase of #160. The following scrapers need their derivation of report_id fixed.

- [x] agriculture
- [x] amtrak
- [x] commerce
- [x] dhs
- [x] education
- [x] eeoc
- [x] exim
- [x] hhs
- [x] hud
- [x] itc
- [x] neh
- [x] nsf
- [x] pbgc
- [x] sba
- [x] sec
- [x] state
- [x] treasury
- [x] lsc
- [x] nasa
- [x] nrc
- [x] fdic
- [x] usaid

For testing, you can run a scraper with `--archive --dry_run --quick`, and then running [unique_report_ids.py](https://raw.githubusercontent.com/divergentdave/inspectors-general/scripts/unique_report_ids.py).

Note that the above script will catch any duplicate report_ids on disk, assuming they are in different years. However, if there's a scraper that uses the same report_id twice in the same year, the second report will clobber the first one. We'll need something like 0a2d33af192a41cd229c5caa2cf59aad67b34634 from #151 to catch those cases at runtime.
Why not an `if ... else` block here?

```python
if landing_url.endswith("/Top-Management-Challenges-FY-2011.aspx"):
    # Testimony!
else:
    report_url_relative = landing_page.select("div.oig_Publications a")[-1].get('href')
```