Replace png flags with use of Twemoji

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

res/css/views/elements/_Dropdown.scss

@@ -77,12 +77,18 @@ limitations under the License.
     white-space: nowrap;
 }
 
-.mx_Dropdown_option img {
+.mx_Dropdown_option img,
+.mx_Dropdown_option .mx_Dropdown_option_emoji {
     margin: 5px;
     width: 16px;
     vertical-align: middle;
 }
 
+.mx_Dropdown_option_emoji {
+    font-size: $font-16px;
+    line-height: $font-16px;
+}
+
 input.mx_Dropdown_option,
 input.mx_Dropdown_option:focus {
     font-weight: normal;