Create gpo_member_photos.py

Needs BeautifulSoup and mechanize. Can pip install. First version downloads images of all members, but only if they have a link to a biography containing their Bioguide ID (365 of 113th's 549 don't). Need to resolve names to IDs for the others using, say, legislators.csv.
Add Bioguide resolution using legislators YAML

If the Bioguide ID isn't found in the member page, resolve it from the values in the YAML file.
Resolves in this sort of order:
last, first
last, first middle
official name
last, nickname
last, first middle-initial.
last followed by , first
ballotopedia name
wikipedia name
last, firstname
last, firstnam
last, firstn
...
last, fi
last, f

Didn't resolve Bioguide IDs for four people.

Bradley, Byrne 113/RP/Bradley -> because GPO has bad data. He's really "Byrne, Bradley".

GPO data should be fixed (how to report?), but should we add a final resolution case for switched names?

These three aren't in the YAML:
Chiesa, Jeff 113/SR/Chiesa
Radel, Trey 113/RP/Radel
Young, C. W. Bill 113/RP/Young

Chiesa left in 2013, Radel left in 2014, Young died in 2013.

TODO: Add caching of downloaded pages, rate limiting.
See https://github.com/unitedstates/congress-legislators/issues/160#issuecomment-34833782
Subset of legislators-current.yaml for testing

test_gpo_member_photos.py uses a subset of exemplar names.
Unit test cases for gpo_member_photos.py

Uses legislators-test.yaml which is a subset of legislators-current.yaml. Could use the full set but it's quicker to load the subset and it contains exemplar entries for each of the test cases.

Run like:
`python test_gpo_member_photos.py`
Also include member URLs containing /RC/ and /DG/
Add caching, special case for BB, rate-limit check

Added caching of member pages.
Added special case for "Bradley, Byrne" - bad GPO data.
Added check in case front page doesn't load, possibly due to rate limiting.
Related: https://github.com/unitedstates/congress-legislators/issues/160
Add rate limiting

--delay is the maximum number of seconds to wait between requests.
Merge pull request #167 from hugovk/master

Add GPO photo scraper