Add some kind of frontend

[fxkr]

Add some kind of frontend, because with the growing number of views it's already getting somewhat confusing.

The relations between the individual views should be integrated into the UI. For example, it should be easy to switch between old and new views, turn change hilighting (when implemented) on and off, turn red/green diff on and off, turn the background on/off, turn poly fills on/off, turn poly fill style fixing on/off, show multiple layers at once etc.

Maybe this could be done as a web UI. That might come in handy later on.

Of course there'll be the question of what to pre-render and what to render on demand.