swiss curves page visualization suggestions

[mcarrara-bioinfo]

After the changes implemented and deployed to resolve issue #791, we received follow-up comments from EAWAG regarding the visualization of the swiss curves. I am including all of them in this issue to start a discussion.

• provide more meaningful middle x-axis tick(s). While the first and last ticks did not raise comments, referring to the beginning and end of time, we received the suggestion to use specific dates for the middle x-axis tick(s), for example using the first of January of each year
• show curves' confidence intervals
• plot the single data points alongside the curve

EAWAG is aware that a decision is dependent on an evaluation of feasibility and readability