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/utils/stringtools.ts

@@ -4,3 +4,7 @@ export function truncateString(str: string, num: number): string {
   }
   return `${str.slice(0, num)}...`;
 }
+
+export function camelize(str: string): any {
+  return str.split('-').map((word, index) => index > 0 ? word.charAt(0).toUpperCase() + word.slice(1) : word).join('');
+}