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/saveload.ts

@@ -1,5 +1,6 @@
 import { findContainerById, MakeIterator } from './itertools';
 import { IEditorState } from '../Interfaces/IEditorState';
+import { IHistoryState } from '../Interfaces/IHistoryState';
 
 /**
  * Revive the Editor state
@@ -14,31 +15,37 @@ export function Revive(editorState: IEditorState): void {
 
   // restore the parents and the selected container
   for (const state of history) {
-    if (state.MainContainer === null || state.MainContainer === undefined) {
-      continue;
-    }
-
-    state.Symbols = new Map(state.Symbols);
-    for (const symbol of state.Symbols.values()) {
-      symbol.linkedContainers = new Set(symbol.linkedContainers);
-    }
-
-    const it = MakeIterator(state.MainContainer);
-    for (const container of it) {
-      const parentId = container.properties.parentId;
-      if (parentId === null) {
-        container.parent = null;
-        continue;
-      }
-      const parent = findContainerById(state.MainContainer, parentId);
-      if (parent === undefined) {
-        continue;
-      }
-      container.parent = parent;
-    }
+    ReviveState(state);
   }
 }
 
+export const ReviveState = (
+  state: IHistoryState
+): void => {
+  if (state.MainContainer === null || state.MainContainer === undefined) {
+    return;
+  }
+
+  state.Symbols = new Map(state.Symbols);
+  for (const symbol of state.Symbols.values()) {
+    symbol.linkedContainers = new Set(symbol.linkedContainers);
+  }
+
+  const it = MakeIterator(state.MainContainer);
+  for (const container of it) {
+    const parentId = container.properties.parentId;
+    if (parentId === null) {
+      container.parent = null;
+      continue;
+    }
+    const parent = findContainerById(state.MainContainer, parentId);
+    if (parent === undefined) {
+      continue;
+    }
+    container.parent = parent;
+  }
+};
+
 export const getCircularReplacer = (): (key: any, value: object | Map<string, any> | null) => object | null | undefined => {
   return (key: any, value: object | null) => {
     if (key === 'parent') {