Add option to not open the socials link on a new page, i.e. for an extra email page

I've added a ``nonewpage`` parameter to social links to avoid popping them open on a new page. This is useful, for example, for adding an email page that is resistant to scraping.

As an example:
``
[[params.social]]
  name = "email"
  url  = "/email"
  nonewpage = true
``

Where /email.md is a page that says something like ``domain at domain dot tld``.

layouts/partials/social-icons.html

@@ -1,3 +1,3 @@
 {{ range . -}}
-    &nbsp; <a href="{{ .url }}" target="_blank" rel="me noopener {{ .rel }}" title="{{ .name | humanize }}">{{ partial "svg.html" . }}</a> &nbsp;
+    &nbsp; <a href="{{ .url }}" {{if eq .nonewpage 0}} target="_blank" {{end}} rel="me noopener {{ .rel }}" title="{{ .name | humanize }}">{{ partial "svg.html" . }}</a> &nbsp;
 {{- end -}}