WIP: Implement class for configuring plugins

This is a temporary commit for creating a MR.

We're using KPlugin XT for configuring Kirogi. But we can't use that for configuring separate plugins. We can use that just for configuring whole application.

We can implement configuration system like that allowing it to manage variables unused, but will be used when some specific plugin is loaded and just ignore them when that plugin is not loaded. But that requires recompilation of configuration system when developer wants to create new plugin. That's not a goal of Kirogi's plugin system.

So i ended up the conclusion that we need some kind of object that is loadable at runtime which manages all of variables the plugin requires.