Update SVG/PNG flags

This PR resolves an issue where some of the country flags that are used
throughout the site appear granulated. It also adds flags that are
missing and optimizes the SVG files by removing metadata, image-editor
related comments/ads, hidden elements, default or non-optimal values and
other stuff that can be safely removed or converted without affecting
the rendering result. Lastly, PNG versions of the flags have been
updated to ensure that they all correctly match the corresponding SVGs.

This will be merged once tests pass.

_sass/screen.scss

@@ -2459,6 +2459,7 @@ br.big {
     width: 40px;
     height: 33px;
     margin-right: 28px;
+    border: 1px solid #dfdfdf;
 }
 .organization-country {
     margin: 0;
@@ -2579,6 +2580,9 @@ br.big {
     height: 33px;
     margin-right: 30px;
 }
+.marketplace-flag {
+    border: 1px solid #dfdfdf;
+}
 .marketplace-link {
     color: #3490E6;
 }