playground: keep state in url/localstorage

[aab-odoo]

Also, maybe remove it from url once it's being edited

[ged-odoo]

Specs

choose a name for localstorage key. For ex, USER_STATE

• add a short key to the code samples: responsive-app, todolist, lifecycle, ...
• whenever the tab selection is changed, add the description to the url: so, it will look like this: https://odoo.github.io/owl/playground/#test. Also, clear localStorage USER_STATE
• whenever the user modifies anything (js/css/xml), the hash changes to #edited
• whenever the page is unloaded, if we are in #edited mode, save to localstorage USER_STATE the js/css/xml
• whenever the app is loaded: check the url
  • if it has a hash, and the hash is #edited, restore state from localStorage USER_STATE (if any). If no state in localstorage, remove hash and go to first code sample
  • if it has a hash and the hash is something else, restore from appropriate code sample (if it exists). if no code sample can be found, remove hash and go to first code sample
  • if it has no hash, go to first code sample