Rewrite UI

[quyse]

Current UI system is not great for the following reasons:

• STM monad needed to create, modify and poll UI.
• Rendering and state processing code are mixed up, no way to make new UI skin.
• Hard to modify or enhance existing controls.
• Hard to make UI depend on actual data.
• UI layout depends on hardcoded sizes in pixels.

There are a few ideas for the new UI:

• Separate code for main state, UI control's state and rendering
• Use pure data structures for states without need of imperative code
• Use lens or other means for easy UI control state's bindings to application's data