Add User-Agent option for Logo Lookup

[randolf-scholz]

Trying to source logos for example from wikipedia can run into:

requests.exceptions.HTTPError: 403 Client Error: Forbidden. Please comply with the User-Agent policy: https://meta.wikimedia.org/wiki/User-Agent_policy

Which states that there must be user-agent information or scripts may be blocked without notice. The expected format is

<client name>/<version> (<contact information>) <library/framework name>/<version> [<library name>/<version> ...]

They provide a template for python:

import requests

url = 'https://example/...'
headers = {'User-Agent': 'CoolBot/0.0 (https://example.org/coolbot/; coolbot@example.org)'}

response = requests.get(url, headers=headers)

Suggestions:

• Add standard header like {'User-Agent': 'pybadges/3.0.0 (https://github.com/google/pybadges/)}
• And/Or add --user-agent option to allow passing this information manually.