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)

public/workers/worker.js

@@ -4,22 +4,19 @@ onmessage = (e) => {
 };
 
 const getCircularReplacer = () => {
-  const seen = new WeakSet();
   return (key, value) => {
     if (key === 'parent') {
       return;
     }
 
-    if (key === 'SelectedContainer') {
-      return;
+    if (key === 'Symbols') {
+      return Array.from(value.entries());
     }
 
-    if (typeof value === 'object' && value !== null) {
-      if (seen.has(value)) {
-        return;
-      }
-      seen.add(value);
+    if (key === 'linkedContainers') {
+      return Array.from(value);
     }
+
     return value;
   };
 };