Webscrapbook

* `server.browse` now defaults to `false`.

* Bumped server requirement to >= 0.3.

* Fixed a security issue that may allow the user to access any directory on Windows.
* Fixed an issue that `file2wsb` converter does not handle a page named `index.html` with a support folder.
* No more generate a title from ID if title is empty for the checker and some converters.
* `file2wsb` converter now generates an item for every normal file.
* `file2wsb` converter now preserves the original filename by default, with an added `--no-preserve-filename` option to tweak the behavior.

* Fixed an issue of crash for `check` if a page has an empty title.
* Renamed converter `migrate0` to `migrate`.
* Added `app.locale` config to determine the locale of the APP theme.
* Added support of downloading a folder or files and folders under a folder for the web interface.
* Added `--data-folder-suffixes` and `--ignore-*-meta` options for `file2wsb` converter.

* Bumped server requirement to >= 0.2.
* Added support of backend server version checking. An error will now be thrown if the backend server version is too old to work with this extension.

* Added support for sidebar and backend server.