fix(admin-ui): Fix background image on login screen

admin-ui/src/app/login/components/login/login.component.scss

@@ -1,7 +1,9 @@
 @import "variables";
 
 .login-wrapper {
-    background-image: url("/assets/dark-triangles.png");
+    // funny url prefix is a work-around for an issue caused by setting the base href.
+    // See https://github.com/angular/angular-cli/issues/4782#issuecomment-423650190
+    background-image: url("~src/assets/dark-triangles.png");
     background-repeat: repeat;
     background-size: auto;
     justify-content: center;