make unaffiliated disclaimer on person layout customizable

[jacobwhall]

This PR allows users to easily change the default disclaimer on the person layout, or disable it altogether. This will help non-OSMUS sites use the built-in person layout more easily.

For example, with unaffiliated_disclaimer and affiliate_orgs set to different values in _config.yml:

unaffiliated_disclaimer: |
  This person is altogther unaffiliated with ACME Mapping Corp., we have no idea who they are.
affiliate_orgs:
  - ACME Mapping Corp

Yields the following, unless of course the user has a role with at: ACME Mapping Corp in their page frontmatter:

To disable to disclaimer, set unaffiliated_disclaimer to false in _config.yml.

[jacobwhall]

@quincylvania I expect we'll be adding quite a few variables to _config.yml (if that's alright with you) to make this theme customizable beyond OSMUS. Maybe we should group some of them together? Here are a couple of ideas mashed together:

_config.yml

socials:
  github: osmus
  twitter: osmus
unaffiliated_disclaimer:
  enabled: true
  message: This is a compilation of publicly-available info...
  exclude_orgs:
    - OpenStreetMap US Staff

Let me know if you have a preference regarding how these get organized, so I can help work toward that goal in my contributions.

Best, Jacob

[quincylvania]

@jacobwhall Thanks for your work on this! I decided to use a simpler approach where you can just put whatever you want in the person footer. (I don't think too many people will need this sort of insider/outsider disclaimer like OSMUS)

I expect we'll be adding quite a few variables to _config.yml (if that's alright with you) to make this theme customizable beyond OSMUS. Maybe we should group some of them together?

This seems reasonable.