refactor social icon logic

[regisphilibert]

We should use the same code (with small alteration) for every social icon as this partial is getting out of hand :)

Something like:

{{ range $social_services }}
{{ with .Param .key }}
<a href="{{ .URL }}" target="_blank" class="link-transition medium link dib z-999 pt3 pt0-l mr1" title="{{ .title }} link" rel="noopener" aria-label="follow on Medium——Opens in a new window">
  {{ partial (printf "svg/%s.svg" ,.key }} (dict "size" $icon_size) }}
  {{- partial "new-window-icon.html" . -}}
</a>
{{ end }}
{{ end }}

Of course with checking that the svg partial exist and fallback on a default etc...

[regisphilibert]

Closed in favor of #422