change home icon image to font awesome icon and changed css accordingly

lms/static/sass/shared/_header.scss

@@ -145,6 +145,14 @@ header.global {
       font-weight: bold;
       letter-spacing: 0;
 
+      .icon {
+        display: inline-block;
+        @include float(left);
+        margin: 3px 0 -3px 0;
+        font-size: 1.2em;
+        color: $m-gray;
+      }
+
       .avatar {
 
         // CASE: right to left layout

lms/templates/navigation.html

@@ -68,7 +68,8 @@ site_status_msg = get_site_status_msg(course_id)
     <ol class="user">
       <li class="primary">
         <a href="${reverse('dashboard')}" class="user-link">
-          <img alt='${_("Dashboard for:")}' class="avatar" src="${settings.STATIC_URL}images/small-header-home-icon.png">
+          <i class="icon fa fa-home" aria-hidden="true"></i>
+          <span class="sr">${_("Dashboard for:")}</span>
           <div>
           ${user.username}
           </div>