1. Add `:event_handler` app option. It is a process that will receive
the app events, the `:open_app`, `{:open_url, url}`, and
`{:open_file, path}` messages.
2. Add `AppBuilder.init/0`. This reads the `APP_BUILDER_INPUT` env
variable which contains the app event the release was started with.
3. Use <https://github.com/wojtekmach/otp/tree/wm-WX_MACOS_NON_GUI_APP>
branch which contains wx fix that hasn't been merged yet.
* Add LIVEBOOK_SHUTDOWN_ENABLED
Previously we relied on code:get_mode(), but since
releases are starting in interactive mode to use
less memory, we need a clearer mechanism.
* Move shutdown feature check to Livebook.Config
Co-authored-by: Jonatan Kłosko <jonatanklosko@gmail.com>
