Add two missing translations

templates/base.html.twig

@@ -47,13 +47,13 @@
                FediPlan -{{ "now"|date("Y") }}
            </div>
            <div class="col-md-4" style="margin-top: 10px; text-align: center;">
-               Author: Thomas<br/>
+               {{ 'common.author'|trans }}: Thomas<br/>
                Mastodon: <a href="https://framapiaf.org/@fedilab" target="_blank">@Fedilab</a><br/>
                Framagit: <a href="https://framagit.org/tom79/" target="_blank">@tom79</a><br/>
                Github: <a href="https://github.com/stom79/" target="_blank">@stom79</a><br/>
            </div>
            <div class="col-md-4" style="margin-top: 10px; text-align: center;">
-               License: <a href="https://www.gnu.org/licenses/gpl-3.0.fr.html" target="_blank">GPL 3</a><br/>
+               {{ 'common.license'|trans }}: <a href="https://www.gnu.org/licenses/gpl-3.0.fr.html" target="_blank">GPL 3</a><br/>
                <a href="https://framagit.org/tom79/fediplan" target="_blank">{{ 'common.source_code'|trans}}</a>
            </div>
        </div>

templates/fediplan/about.html.twig

@@ -4,7 +4,7 @@
 
 {% block content %}
     {% include 'nav.html.twig' %}
-    <h1>About</h1>
+    <h1>{{ 'common.about'|trans }}</h1>
 
     <div class="row well">
         <div class="col-md-8 jumbotron">

translations/fediplan.en.yaml

@@ -19,6 +19,8 @@ common:
   proceed_confirm: Do you want to proceed?
   start_upload: Start upload
   counter: Counter
+  license: License
+  author: Author
 status:
   visibility:
     public: Public