Webscrapbook

* Switched backend server framework to `Flask` from `Bottle`.
* Added support for `app.allow_x_*` configs to prevent issues when serving behind a reverse proxy.
* Dropped support for `server.ssl_pw` config.

* Added support of zip editing through server actions.

* Added support for `book.*.no_tree` config.

* Added `lock` and `unlock` actions.
* Merged `upload` action into `save`.

* Added `wsbview` CLI executable.

* First public release.


Changelog
* This project generally follows [semantic versioning](https://semver.org/). For a version `x.y.z`, `x` means a major (backward incompatible) change, `y` means a minor (backward compatible) change, and `z` means a patch (bug fix). Few versions may not strictly follow this rule due to historical reasons, though.
* Versions before 1.0 are in initial development. APIs are not stable for these versions, even a `y` version can involve a breaking change, and only partial notable changes are summarized in this document. See full commit history in the source repository for details.
* Backend server requirement in this document refers to the version of [`webscrapbook` Python package](https://github.com/danny0838/pywebscrapbook) (or PyWebScrapBook).