Responsive layout tweaks

The emoji toolbar now needs more space due to the skintone selector.
Ensure that there is enough space to display the selector.
Set min-width on the entire messenger to 440px.

src/sass/layout/_main.scss

@@ -43,6 +43,7 @@
     border-radius: $material-radius;
     box-shadow: $material-card-shadow;
     width: 100%;
+    min-width: 440px;
     height: 100%;
     overflow: hidden;
 }

src/sass/layout/_responsive.scss

@@ -22,7 +22,13 @@
     }
 }
 
-@media (max-width: 600px) {
+@media (max-width: 750px) {
+    .twemoji-picker .tab label img {
+        margin: 3px 0 0 !important;
+    }
+}
+
+@media (max-width: 630px) {
     #messenger {
         &.show-detail {
             #navigation {