Add plugin mechanism and support corresponding options in self-configuration

[StrayDragon]

Let me see... 🤔 (wait for updating)

[StrayDragon]

Plugins will from:

• Some are user-written local plug-ins or scripts
• Some from remote plugins store ?

A bundle of candidate sub-commands like:

create/edit # |
add/install/load/upload # +
upgrade/update # ^
remove/uninstall/unload # -

[StrayDragon]

Now, tweedle has a very nice plug-in mechanism, benefit by click-contrib/click-plugins

The config system is WIP