Define remark host in runtime (#325)

* convert closest-polyfill to ts

* make remark respect host property in client setup

frontend/app/utils/parseQuery.ts

@@ -0,0 +1,22 @@
+/** converts widnow.location.search into object */
+export function parseQuery(search: string): { [key: string]: string } {
+  if (search.length < 2) return {};
+  return search
+    .substr(1)
+    .split('&')
+    .map(
+      (chunk): [string, string] => {
+        const parts = chunk.split('=');
+        if (parts.length < 2) {
+          parts[1] = '';
+        } else {
+          parts[1] = decodeURIComponent(parts[1]);
+        }
+        return parts as [string, string];
+      }
+    )
+    .reduce<{ [key: string]: string }>((c, x) => {
+      c[x[0]] = x[1];
+      return c;
+    }, {});
+}