Javascript cleanup

[joto]

The Javascript code is a bit of a mess. I am not a big Javascript expert, but I am sure some code could be cleaned up and made more modular.

Here are some more specific bits to work on:

• jQuery is used in parts of the application but I have started phasing it out. Modern browsers natively support most of what jQuery used to provide. Some code from OpenLayers or D3 which are included anyway could be used as helpers, for instance with AJAX requests.
• We don't need to include all of OpenLayers but should create a special build of OL only with the needed parts.
• Some code might be put into an extension for OpenLayers.

The goal here is to get clean, simple and fast JS code. It is definitely not a goal to use some complex JS framework, especially when this means that the application would need to be "built" before it can be used. On the whole the application is simple enough that something like this isn't needed.

[joto]

I have removed jQuery completely using native JS code. The ajax JSON request now use the D3 library.