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/Interfaces/IContainerModel.ts

@@ -1,21 +1,25 @@
-import IProperties from './IProperties';
+import IContainerProperties from './IContainerProperties';
 
 export interface IContainerModel {
   children: IContainerModel[]
   parent: IContainerModel | null
-  properties: IProperties
+  properties: IContainerProperties
   userData: Record<string, string | number>
 }
 
+/**
+ * Macro for creating the interface
+ * Do not add methods since they will be lost during serialization
+ */
 export class ContainerModel implements IContainerModel {
   public children: IContainerModel[];
   public parent: IContainerModel | null;
-  public properties: IProperties;
+  public properties: IContainerProperties;
   public userData: Record<string, string | number>;
 
   constructor(
     parent: IContainerModel | null,
-    properties: IProperties,
+    properties: IContainerProperties,
     children: IContainerModel[] = [],
     userData = {}) {
     this.parent = parent;