Promote reply button up to message action bar

This moves the reply action out of the existing options menu and up to the
message action bar for easier access.

res/css/views/messages/_MessageActionBar.scss

@@ -55,8 +55,8 @@ limitations under the License.
             position: absolute;
             top: 0;
             left: 0;
-            bottom: 0;
-            right: 0;
+            height: 100%;
+            width: 100%;
             mask-repeat: no-repeat;
             mask-position: center;
             background-color: $primary-fg-color;
@@ -64,6 +64,10 @@ limitations under the License.
     }
 }
 
+.mx_MessageActionBar_replyButton::after {
+    mask-image: url('$(res)/img/reply.svg');
+}
+
 .mx_MessageActionBar_optionsButton::after {
     mask-image: url('$(res)/img/icon_context.svg');
 }