Webscrapbook

* Fixed an issue that `Capture tabs` like actions in the context menu of a tab does not apply to all selected tabs.
* Fixed an issue that item locating does not work in Firefox < 59.

* Remove obsolete debug code.

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

* Bumped client requirement to >= 2.0.1.
* Added CLI and web API for scrapbook querying and searching.
* Added support of `book.*.new_at_top` config.
* Reworked `cache` API: added `book.*.inclusive_frames`, `book.*.static_index`, `book.*.rss_root`, and `book.*.rss_item_count` configs and `--rss` option in place of the `--inclusive-frames`, `--rss-root`, and `--rss-item-count` options.
* Reworked `cache` and `convert items` CLI utilities to support specifying items for each book.
* Reworked `export` and `import` with new version 2 archive file format, which supports better tree reconstruction for multi-referenced items, and fixed many issues.
* Reworked `encrypt` and authorization related configs to support stronger password protection.
* Reworked internal API for several modules.
* Miscellaneous bug fixes, documentation improvement, and optimization and refactoring of the source code and the unittest suite.

* 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.