added urlQueryParameter helper function

src/mol-util/url-query.ts

+/**
+ * Copyright (c) 2018 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ *
+ * @author Alexander Rose <alexander.rose@weirdbyte.de>
+ */
+
+export function urlQueryParameter (id: string) {
+    if (typeof window === 'undefined') return undefined
+    const a = new RegExp(`${id}=([^&#=]*)`)
+    const m = a.exec(window.location.search)
+    return m ? decodeURIComponent(m[1]) : undefined
+}
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