Webscrapbook

* Fixed script error in Chromium < 80 and Firefox < 74.

* Bumped server requirement to >= 2.0.1.
* Reworked scrapbook search as server sided.
* Optimized several scrapbook operations using new server-sided API.
* Added support of recent picked items for the item picker of the details dialog.
* Added support of erasing elements with XPath.
* Added support of permanently deleting item(s) by holding shift when performing a `Remove`.
* Added `Empty recycle bin` command.
* Added support of item exporting/importing.
* Added new options `scrapbook.autoCache.fulltextCache` and `scrapbook.autoCache.createStaticSite` for automatic cache update.
* Fulltext cache is now updated automatically when creating a new note or uploading files.
* Adjusted DnD effect for the sidebar tree.
* Improved UI for modal dialogs.

* Fixed some potential errors for the unittest suite.
* Fixed inconsistent MIME type for `*.swf` files on some platforms.
* No more adjust the timestamp of the imported files automatically.

* Updated dependency to `Flask >= 2.0.0` and `Werkzeug >= 2.0.1`.
* Fixed some compatibility issues for Werkzeug >= 2.3.

* Fixed an issue that erasing by selector may remove the custom elements loader.

* Fixed misbehaving tree scrollbar for the item picker dialog.