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/SymbolLayer.tsx

@@ -0,0 +1,23 @@
+import * as React from 'react';
+import { ISymbolModel } from '../../../Interfaces/ISymbolModel';
+import { Symbol } from './Symbol';
+
+interface ISymbolLayerProps {
+  symbols: Map<string, ISymbolModel>
+}
+
+export const SymbolLayer: React.FC<ISymbolLayerProps> = (props) => {
+  const symbols: JSX.Element[] = [];
+  props.symbols.forEach((symbol) => {
+    symbols.push(
+      <Symbol key={`symbol-${symbol.id}`} model={symbol} />
+    );
+  });
+  return (
+    <g>
+      {
+        symbols
+      }
+    </g>
+  );
+};