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/Editor/Behaviors/AnchorBehaviors.ts

@@ -28,7 +28,7 @@ export function ApplyAnchor(container: IContainerModel): IContainerModel {
   }
 
   const rigidBodies = container.parent.children.filter(
-    child => child.properties.isRigidBody && !child.properties.isAnchor
+    child => !child.properties.isAnchor
   );
 
   const overlappingContainers = getOverlappingContainers(container, rigidBodies);