Add social buttons: Publons, ResearchGate and Blogger (alshedivat#65)

* Add social button: Publons

* Add social button: ResearchGate

* Add social button: Blogger

Author: g-oikonomou

_config.yml

@@ -24,6 +24,9 @@ scholar_userid: # your Google Scholar ID
 orcid_id: # your ORCID ID
 medium_username: # your Medium username
 quora_username: # your Quora username
+publons_id: # your ID on Publons
+research_gate_profile: # your profile on ResearchGate
+blogger_url: # your blogger URL
 
 contact_note: >
   You can even add a little note about which of these is the best way to reach you.

_includes/social.html

@@ -3,12 +3,15 @@
     {% if site.email %}<a href="mailto:{{ site.email | encode_email }}"><i class="fas fa-envelope"></i></a>{% endif %}
     {% if site.orcid_id %}<a href="https://orcid.org/{{ site.orcid_id }}" target="_blank" title="ORCID"><i class="ai ai-orcid"></i></a>{% endif %}
     {% if site.scholar_userid %}<a href="https://scholar.google.com/citations?user={{ site.scholar_userid }}" target="_blank" title="Google Scholar"><i class="ai ai-google-scholar"></i></a>{% endif %}
+    {% if site.publons_id %}<a href="https://publons.com/a/{{ site.publons_id }}/" target="_blank" title="Publons"><i class="ai ai-publons"></i></a>{% endif %}
+    {% if site.research_gate_profile %}<a href="https://www.researchgate.net/profile/{{site.research_gate_profile}}/" target="_blank" title="ResearchGate"><i class="ai ai-researchgate"></i></a>{% endif %}
     {% if site.github_username %}<a href="https://github.com/{{ site.github_username }}" target="_blank" title="GitHub"><i class="fab fa-github"></i></a>{% endif %}
     {% if site.linkedin_username %}<a href="https://www.linkedin.com/in/{{ site.linkedin_username }}" target="_blank" title="LinkedIn"><i class="fab fa-linkedin"></i></a>{% endif %}
     {% if site.twitter_username %}<a href="https://twitter.com/{{ site.twitter_username }}" target="_blank" title="Twitter"><i class="fab fa-twitter"></i></a>{% endif %}
     {% if site.strava_userid %}<a href="https://www.strava.com/athletes/{{ site.strava_userid }}" target="_blank" title="Strava"><i class="fab fa-strava"></i></a>{% endif %}
     {% if site.medium_username %}<a href="https://medium.com/@{{ site.medium_username }}" target="_blank" title="Medium"><i class="fab fa-medium"></i></a>{% endif %}
     {% if site.quora_username %}<a href="https://www.quora.com/profile/{{ site.quora_username }}" target="_blank" title="Quora"><i class="fab fa-quora"></i></a>{% endif %}
+    {% if site.blogger_url %}<a href="{{ site.blogger_url }}" target="_blank" title="Blogger"><i class="fab fa-blogger-b"></i></a>{% endif %}
   </span>
 
   <div class="col three caption">