Merged PR 179: Fix bugs about flex and context menu (see desc) + disable hard rigid behavior + add missing properties to form + Clean up css

- Clean up some css class
- Fix wrong order when applying flex
- Fix Replace behavior not working because previous container was still existing
- Disable hard rigid behavior which disallow two container to overlap
- Add ENABLE_FLEX, ENABLE_HARD_RIGID ENABLE_SWAP
- Add missing form properties with dimensions
- Update readme

src/Components/App/App.tsx

@@ -1,5 +1,4 @@
 import React, { Dispatch, SetStateAction, useEffect, useState } from 'react';
-import './App.scss';
 import { MainMenu } from '../MainMenu/MainMenu';
 import { ContainerModel } from '../../Interfaces/IContainerModel';
 import { Editor } from '../Editor/Editor';
@@ -78,7 +77,7 @@ export function App(props: IAppProps): JSX.Element {
   }
 
   return (
-    <div className='bg-blue-100 h-full w-full'>
+    <div className='mainmenu-bg'>
       <MainMenu
         newEditor={() => NewEditor(
           setEditorState, setLoaded