Adding mask and toggle for Card Security Code (#5)

* Adding mask and toggle for Card Security Code

* For Card Code Mask - show same number of characters as code

src/models/view/cardView.ts

@@ -18,6 +18,10 @@ export class CardView implements View {
         // ctor
     }
 
+    get maskedCode(): string {
+        return this.code != null ? '•'.repeat(this.code.length) : null;
+    }
+
     get brand(): string {
         return this._brand;
     }