WIP: plugin spec

[Lunarequest]

I'm working on plugin support for archinstall, so far this is the plugin layout I have come up with. all plugins will be loaded by the Installer class. when a plugin is loaded successfully a on_load function will be called, this will be when the Installer class is created. post_pacstrap which called right after the pacstrap function finally post_install this is called after minimal install is completed

[svartkanin]

@Torxed shall we close this for the time being as there haven't been any updates in a while