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/SVG/Elements/Selector.tsx

@@ -3,7 +3,7 @@ import { IContainerModel } from '../../../Interfaces/IContainerModel';
 import { getAbsolutePosition } from '../../../utils/itertools';
 
 interface ISelectorProps {
-  selected: IContainerModel | null
+  selected?: IContainerModel
 }
 
 export const Selector: React.FC<ISelectorProps> = (props) => {