Add GitLab button to footer in mobile layout.

assets/css/styles.css

@@ -150,15 +150,14 @@ figcaption {
 
 #signup2 {display:none;}
 
-#twitter {
+.twitter {
     float:right;
-    padding-left:12px;
+    margin-left:12px;
 }
 
-#twitter2 {
+.twitter2 {
     float:left;
-    padding-left:15px;
-    padding-right:12px;
+    margin-left:12px;
 }
 
 #signupform {
@@ -172,6 +171,7 @@ figcaption {
     height:30px;
     float:left;
     text-align:left;
+    margin-left: 12px;
 }
 
 #signupconf {

themes/briar/layouts/partials/footer.html

  <div id="footer_container">
     <div id="footer">
       <div id="signup2">
-        <div id="twitter2">
-          <a href="https://twitter.com/BriarApp" rel="noopener noreferrer"><img class="twitterbutton" src="/img/twitter.png" alt="Small logo of twitter"/></a>
-        </div> <!-- twitter2 -->
+        <div class="twitter2">
+          <a href="https://code.briarproject.org/briar" rel="noopener noreferrer"><img class="twitterbutton" src="/img/gitlab.png" alt="Small GitLab logo"/></a>
+        </div>
+        <div class="twitter2">
+          <a href="https://twitter.com/BriarApp" rel="noopener noreferrer"><img class="twitterbutton" src="/img/twitter.png" alt="Small Twitter logo"/></a>
+        </div>
         <form id="signupform2" action="https://sourceforge.net/projects/briar/lists/briar-announce" rel="noopener noreferrer" method="get" onSubmit="submitForm2()">
           <input placeholder="Email address" type="email" name="email" tabindex="2"/>
           <button name="submit" type="submit" id="signup-submit2">Keep me updated</button>

themes/briar/layouts/partials/header.html

@@ -3,12 +3,12 @@
         <a href="/"><div id="logo"><img src="/img/briar_logo_large.png" alt="Briar" class="logo"/></div></a>
         <div id="nav">
           <div id="signup">
-            <div id="twitter">
+            <div class="twitter">
               <a href="https://code.briarproject.org/briar" rel="noopener noreferrer"><img class="twitterbutton" src="/img/gitlab.png" alt="Small GitLab logo"/></a>
-            </div> <!-- GitLab -->
-            <div id="twitter">
-              <a href="https://twitter.com/BriarApp" rel="noopener noreferrer"><img class="twitterbutton" src="/img/twitter.png" alt="Small twitter logo"/></a>
-            </div> <!-- twitter -->
+            </div>
+            <div class="twitter">
+              <a href="https://twitter.com/BriarApp" rel="noopener noreferrer"><img class="twitterbutton" src="/img/twitter.png" alt="Small Twitter logo"/></a>
+            </div>
             <form id="signupform" action="https://sourceforge.net/projects/briar/lists/briar-announce" rel="noopener noreferrer" method="get" onSubmit="submitForm()">
               <input placeholder="Email address" type="email" name="email" tabindex="2"/>
               <button name="submit" type="submit" id="signup-submit">Keep me updated</button>