Time scales

implements #10 (closed)

Add buttons to each page/functionality which will allow the user to change the period from which the data ale loaded.

Several mechanisms including dynamic content loading had to introduced.

I also ask the reviewer to polish some mainly graphic-related issues which I'm not so skilled in.

Finally I recommend the reviewer to read the MR commit by commit as it is quite complex and I did my best to split it into commits very systematically.