Add Plot title with dataset information

[153957]

Requested by Mark Dirken:
Add information to the plot (on canvas) about which dataset was used to create it.
i.e. the station and dates (in some compact way).
This way people should be able to easily keep track of what their plots are off.

One of the milestones for flot 0.9 is:

• Core support for axis labels and plot titles.

So perhaps we should just wait until that work to implement this.