class to center an image as a block element

this is effectively a replacement for div.splash means of getting a
centered header image, and can be used anywhere

incorporealcms/static/css/style.css

@@ -131,6 +131,12 @@ img {
     max-width: 50% !important;
 }
 
+.img-center {
+    display: block;
+    margin-left: auto;
+    margin-right: auto;
+}
+
 /* For screens with width smaller than 400px */
 .figure-left .figure-right {
     max-width: 95%;