Better user experience.

• When a link is clicked in the header nav bar, the page is no longer refreshed, only the page-content is updated so the user doesn't have to reload everything
• Another small change but very significant and has a high impact in user experience is that, for each page upon loading, a default figure is rendered. Before this, we had to wait for the callback to fire before rendering the default graph, and for each page callback we have to check it a currently rendered graph exists. This is no longer the case, the user experience is significantly improved.
• Massive modifications in code style and naming conventions