Added a certificaterunner class

ref #1

src/models/CertificateRunner.ts

@@ -0,0 +1,23 @@
+import {
+    IsArray,
+    IsInt
+} from "class-validator";
+import { Runner } from './Runner';
+
+/**
+ * Defines the certificate runner class (from which the runner certificates get generated).
+*/
+export class CertificateRunner extends Runner {
+
+    /**
+     * The total distance ran by the runner.
+     */
+    @IsInt()
+    distance: number;
+
+    /**
+     * Array containing all distance donations associated with the runner.
+     */
+    @IsArray()
+    distanceDonations: any[];
+}