feat(form): add (auto)save and local schema repo

[miguelgrc]

• Adds an autosave feature (into localStorage as formuleCurrent). When reloading the page or closing and opening the browser the last state will be loaded automatically
• Adds the following features in a floating menu in formule-demo:
  • Manual save: with a ctrl+s shortcut as well (into localStorage as formuleForm_<formid>). It shows a badge when there are unsaved changes
  • Load schemas: new drawer listing all the schemas currently stored in localStorage, lets you delete, download and upload schemas
  • Revert: reverts unsaved changes
  • New schema: starts a new schema from scratch
  • View schema: the existing schema viewer has been moved into here
• Although this menu is exclusive for the demo, the logic of the saving/loading features mentioned above has been implemented and exported from formule as functions so they can be used in any project.
• The form key is now displayed in the SchemaPreview. It can be disabled with hideSchemaKey.
• The process of initializing the form has been simplified, now it's not needed to call initFormuleSchema() in a useEffect on first render anymore (you can still do it on demand or if you want to load an existing form).