Merged PR 162: Implement symbols and other stuff (see desc)

Implement symbols
- Add, Remove, Select Container
- Form
- Link with container
- Symbol behavior application to container (move to x with xpositionreference)

Important changes
- Remove SelectedContainer from HistoryState, meaning that it will be slower for each load but will be faster for each operations* (SetHistory, SelectContainer, DeleteContainer, SymbolOperations)
- ElementsSidebar now opens with isSidebarOpen meaning that both sidebar will open on toggle
- Moved camelize, transformX, restoreX to different modules (stringtools.ts, svg.ts)

src/Components/App/App.tsx

@@ -26,9 +26,10 @@ export const App: React.FunctionComponent<IAppProps> = (props) => {
     history: [{
       LastAction: '',
       MainContainer: defaultMainContainer,
-      SelectedContainer: defaultMainContainer,
       SelectedContainerId: defaultMainContainer.properties.id,
-      TypeCounters: {}
+      TypeCounters: {},
+      Symbols: new Map(),
+      SelectedSymbolId: ''
     }],
     historyCurrentStep: 0
   });