Implement anchor and fix bugs with rigid body (#27)

Co-authored-by: Eric NGUYEN <enguyen@techform.fr>
Reviewed-on: https://git.siklos-chaneru.duckdns.org/Siklos/svg-layout-designer-react/pulls/27

src/Interfaces/IProperties.ts

@@ -1,11 +1,21 @@
 import * as React from 'react';
 import { XPositionReference } from '../Enums/XPositionReference';
 
+/**
+ * Properties of a container
+ * @property id id of the container
+ * @property parentId id of the parent container
+ * @property x horizontal offset of the container
+ * @property y vertical offset of the container
+ * @property isRigidBody if true apply rigid body behaviors
+ * @property isAnchor if true apply anchor behaviors
+ */
 export default interface IProperties extends React.CSSProperties {
   id: string
   parentId: string | null
   x: number
   y: number
   isRigidBody: boolean
+  isAnchor: boolean
   XPositionReference?: XPositionReference
 }