Remove gui specific code

[ivmartel]

GUI code should go in dwvs' client code to limit dwv responsibilities.

[ivmartel]

With this change, comes a big change in the logic of the app, dwv tries to do as less as possible html manipulation.

Concretely, this means:

• tools do not handle their gui anymore
• the application does not initialise the tool guis
• no more overlay setting while loading data
• (in application.js) no more public event handlers (apart from the key handler, it could also go)

Conclusion, way less gui code in the gui folder and a more focused app!