added isInteger helper

src/mol-util/number.ts

@@ -46,4 +46,10 @@ export function getArrayDigitCount(xs: ArrayLike<number>, maxDigits: number, del
         }
     }
     return { mantissaDigits, integerDigits };
+}
+
+export function isInteger(s: string) {
+    s = s.trim()
+    const n = parseInt(s, 10)
+    return isNaN(n) ? false : n.toString() === s
 }