Merged PR 167: Add Flex and fix bugs (read desc)

Note: The branch name does not fit the new features.

- Implement Flex with simplex
- Enable rigid body by default (removed IsRigidBody property) <=== possibly a bad idea
- Sort children in add and update properties
- Implement MaxWidth
- Add more docs

Fixes :
- .env.production url
- Symbols: not blocking the linked container when the parent is moving

src/Components/SVG/Elements/Selector.tsx

@@ -1,6 +1,7 @@
 import * as React from 'react';
 import { IContainerModel } from '../../../Interfaces/IContainerModel';
 import { getAbsolutePosition } from '../../../utils/itertools';
+import { RemoveMargin } from '../../../utils/svg';
 
 interface ISelectorProps {
   selected?: IContainerModel
@@ -14,11 +15,19 @@ export const Selector: React.FC<ISelectorProps> = (props) => {
     );
   }
 
-  const [x, y] = getAbsolutePosition(props.selected);
-  const [width, height] = [
+  let [x, y] = getAbsolutePosition(props.selected);
+  let [width, height] = [
     props.selected.properties.width,
     props.selected.properties.height
   ];
+
+  ({ x, y, width, height } = RemoveMargin(x, y, width, height,
+    props.selected.properties.margin.left,
+    props.selected.properties.margin.bottom,
+    props.selected.properties.margin.top,
+    props.selected.properties.margin.right
+  ));
+
   const style: React.CSSProperties = {
     stroke: '#3B82F6', // tw blue-500
     strokeWidth: 4,