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/utils/svg.ts

@@ -1,5 +1,15 @@
 import { XPositionReference } from '../Enums/XPositionReference';
 
+// TODO: Big refactoring
+/**
+ * TODO:
+ * All of these methods should have been
+ * inside ContainerModel class
+ * But because of serialization, the methods are lost.
+ * Rather than adding more functions to this class,
+ * it is better to fix serialization with the reviver.
+ */
+
 export function transformX(x: number, width: number, xPositionReference = XPositionReference.Left): number {
   let transformedX = x;
   if (xPositionReference === XPositionReference.Center) {
@@ -19,3 +29,69 @@ export function restoreX(x: number, width: number, xPositionReference = XPositio
   }
   return transformedX;
 }
+
+export function ApplyMargin(
+  x: number,
+  y: number,
+  width: number,
+  height: number,
+  left?: number,
+  bottom?: number,
+  top?: number,
+  right?: number
+): { x: number, y: number, width: number, height: number } {
+  left = left ?? 0;
+  right = right ?? 0;
+  bottom = bottom ?? 0;
+  top = top ?? 0;
+  x = ApplyXMargin(x, left);
+  y += top;
+  width = ApplyWidthMargin(width, left, right);
+  height -= (bottom + top);
+  return { x, y, width, height };
+}
+
+export function RemoveMargin(
+  x: number,
+  y: number,
+  width: number,
+  height: number,
+  left?: number,
+  bottom?: number,
+  top?: number,
+  right?: number
+): { x: number, y: number, width: number, height: number } {
+  bottom = bottom ?? 0;
+  top = top ?? 0;
+  x = RemoveXMargin(x, left);
+  y -= top;
+  width = RemoveWidthMargin(width, left, right);
+  height += (bottom + top);
+  return { x, y, width, height };
+}
+
+export function ApplyXMargin(x: number, left?: number): number {
+  left = left ?? 0;
+  x += left;
+  return x;
+}
+
+export function RemoveXMargin(x: number, left?: number): number {
+  left = left ?? 0;
+  x -= left;
+  return x;
+}
+
+export function ApplyWidthMargin(width: number, left?: number, right?: number): number {
+  left = left ?? 0;
+  right = right ?? 0;
+  width -= (left + right);
+  return width;
+}
+
+export function RemoveWidthMargin(width: number, left?: number, right?: number): number {
+  left = left ?? 0;
+  right = right ?? 0;
+  width += (left + right);
+  return width;
+}