Webscrapbook

* Added support of capturing the source document embedded through an `<object>` tag.
* No more save XHTML or SVG files as srcdoc when saving as single HTML.

* Improved config checking of capture helpers and auto-capture to prevent more possible bad input.
* Fixed an issue that unfetchable resources are not skipped during internalization.
* Fixed an error when internalizaing a single HTML item. Internalized resources are now saved as data URLs in such case.

* Capture the original page rather than the meta refreshed target page if the meta refresh time is non-zero.
* Improved the tooltips about auto-capture.
* Adjusted handling of some HTTP headers and HTML attributes to conform with the spec better.
* Fixed some potential errors for ASCII whitespace handling.
* Fixed a potential error handling for nested svg and math elements.

* Preloads and prefetches are now removed by default, with a new option `capture.preload` to tweak the behavior.
* Shadow DOMs are saved as `data-scrapbook-shadowdom` attribute in place of `data-scrapbook-shadowroot`, with simplified data structure and smaller size.

* Hash part of source URL is now considered when viewing an item.
* Fixed an issue that URL hash is not included in the source URL for the captured item.
* Fixed several issues on handling an item whose index file is an archive.

* Added support of more modes for `Form status` capture option.
* Added a default option for the backend server URL option.
* Added support of enabling/disabling undo feature from its context menu.
* Added support of `Home` and `End` for sidebar key navigation.
* Added a message for a scrapbook configured as `no_tree` in the sidebar.
* Added support of `limit:` command for search.
* Fixed an issue that certain interactive properties, such as form status, canvas, and shadow DOM, are lost after an unerase in a re-loaded document.
* Fixed an issue that unrelated content in the document be refreshed after an undo.
* Fixed an issue that certain interactive properties, such as canvas and shadow DOM, are lost after an undo.
* Fixed missing support of opening in new tab for `View index page` sidebar command.
* Fixed an issue that the opened postit is not saved when switching scrapbook.
* Fixed an issue that switching scrapbook after a change of server config can load incorrect tree data.
* Fixed an error causing the copy item dialog in a manage dialog not working.
* Fixed an error causing unit tests not working.