Webscrapbook

* Changed view status caching format for sidebar to avoid a comflict within different views.
* Added support of top-level null value for *.js tree files.

* Added a capture option to specify delay time before capturing an auto-launching tab.
* Added a capture option to insert an infobar.
* Improved capture helpers:
* Added `name` and `debug` properties.
* Added `options` and `insert` commands.
* Added support to debug a capture helper commands using `*` prefix.
* Improved error reporting.
* Improved sidebar and manage dialog:
* Adjusted command button to show scrapbook-related commands rather than echo the context menu.
* Added `Search within` command to sidebar.
* Added `Recover` command for a recycle bin to sidebar.

* Reworked editor toolbar:
* Added context menu in place of sub-menu buttons. This prevents toolbar overflow on mobile browsers.
* Enlarged toolbar and buttons.

* Bumped server requirement to >= 0.23.
* Reworked site indexer:
* Moved site indexer button from browser action to options page.
* Shifted site indexer to server-side, with greatly improved performance, and minor format change. (Consider recreate fulltext cache.)
* Automatically update fulltext cache when a web page or note is captured or edited.
* Added data checker. Moved the feature of importing non-indexed web page files through site indexer to data checker.
* Dropped support of site indexing through dragging and dropping local filesystem folders or ZIP files.
* Dropped support of importing legacy ScrapBook data through site indexer. (Use `wsb convert sb2wsb` of PyWebScrapBook instead.)
* Added `disabled` capture helper property.

* Added `Accept` header for requests to the backend server. This allows the reverse proxy server or upper server to response with a more appropriate format to the client.

* Added support of self version checking. An error will now be thrown if the extension version is too old to work with the corresponding backend server.
* A request for acquiring an access token now uses a POST rather than GET method.