css: use less blurry icon for external link

Your mileage may vary, but for me the old icon looks blurry. The new
one is character 0xf08e from OTF font awsome in size 10.
The icon color is black, gray level is adjusted via opacity.

Signed-off-by: Christian Hesse <mail@eworm.de>

cgit.css

@@ -86,7 +86,8 @@ div#cgit table.tabs td a.active {
 }
 
 div#cgit table.tabs a[href^="http://"]:after, div#cgit table.tabs a[href^="https://"]:after {
-	content: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAQAAAAnOwc2AAAAAnNCSVQICFXsRgQAAAAJcEhZcwAAABQAAAAUAVyMgXwAAAAZdEVYdFNvZnR3YXJlAHd3dy5pbmtzY2FwZS5vcmeb7jwaAAAAeklEQVQI12NoYCu3q3ABwXL98vTy/0D4jaF8XXldRRoYejAwlu8BCTOU72SAg4q08j/le0GC22BC5anlfyrSGBiBGCZYllz+pywLJg8WLOMtf1GeCjRgI5IgSBhMboUIHq40r1CCQrfyDRAV6uXdZTMhsKKlVIIBFwAAVeg4KFYK95cAAAAASUVORK5CYII=);
+	content: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAQAAAAnOwc2AAAAAmJLR0QA/4ePzL8AAAAJcEhZcwAACxMAAAsTAQCanBgAAAAHdElNRQfgAhcJDQY+gm2TAAAAHWlUWHRDb21tZW50AAAAAABDcmVhdGVkIHdpdGggR0lNUGQuZQcAAABbSURBVAhbY2BABs4MU4CwhYHBh2Erww4wrGFQZHjI8B8IgUIscJWyDHcggltQhI4zGDCcRwhChPggHIggP1QoAVmQkSETrGoHsiAEsACtBYN0oDAMbgU6EBcAAL2eHUt4XUU4AAAAAElFTkSuQmCC);
+	opacity: 0.5;
 	margin: 0 0 0 5px;
 }