Add flag to acknowledge all alerts.
This is a database that is updated by github hooks and a web interface (written in flask) that displays current review status of pull requests in all repos tracked by harold.
Giving a default value to an argument of a plugin's `make_plugin` makes that dependency optional. If the plugin resolver can't find an appropriate plugin of that name, it will give `make_plugin` the default value instead.
This is better separation of concerns and allows the config parser to be used outside of a harold context more readily.
It's more compatible across the board and we can set permissions accordingly.