Code + comment cleanup for the entities

ref #39

src/models/entities/UserGroup.ts

@@ -9,7 +9,8 @@ import { ResponseUserGroup } from '../responses/ResponseUserGroup';
 import { Principal } from './Principal';
 
 /**
- * Defines the UserGroup interface.
+ * Defines the UserGroup entity.
+ * This entity describes a group of users with a set of permissions.
 */
 @ChildEntity()
 export class UserGroup extends Principal {
@@ -30,6 +31,9 @@ export class UserGroup extends Principal {
   @IsString()
   description?: string;
 
+  /**
+   * Turns this entity into it's response class.
+   */
   public toResponse(): ResponsePrincipal {
     return new ResponseUserGroup(this);
   }