Regardless of their start date, vacancies should be shown last. This
means that the team page won't intersperse vacancies and current
GitLabbers, and we can set the start_date for the new vacancies
correctly.

1. Normalize `US` to `United States`
2. Group team members by their normalized country
3. Minor style fixes

This adds two helpers, `direct_team` and `stable_counterparts`. By using these
in a template (for example, changing an .html.md file to be .html.md.erb), it's
possible to display a table of team members without copying and pasting from
team.yml.

`direct_team` renders a table of the people who report directly to a person with
a particular title, including the manager. (The manager is always listed first.)

`stable_counterparts` lists people whose titles match a regex (for instance,
those whose titles end in 'Plan'), and excludes anyone in the direct team to
avoid duplicating entries.

Apart from the manager being first in `direct_team`, both of these are otherwise
in the order of appearance in team.yml.

Closes #2449

It is hightly unlikely that team member can have a duplicated anchor on
the team page, so let's remove the code responsible for handling
duplicates.