Added the runnerteam class

ref #11

src/models/RunnerTeam.ts

@@ -0,0 +1,19 @@
+import { Entity, Column } from "typeorm";
+import { IsNotEmpty } from "class-validator";
+import { RunnerGroup } from "./RunnerGroup";
+
+/**
+ * Defines a runner team (class or deparment for example).
+*/
+@Entity()
+export class RunnerTeam extends RunnerGroup {
+
+  /**
+   * The team's parent group.
+   * Optional
+   */
+  @Column()
+  @IsNotEmpty()
+  //TODO: Relationship
+  parentGroup?: RunnerGroup;
+}