PlotForecastPDF Multiple observations

hi @nperez @llledo,

I have seen that I forgot to create the issue corresponding to the new branch "develop-multiple-observations". This branch has been created because on a specific project different years of observation in each pannel are needed.

I managed to issue the plot like this:

Because of running out of time I could not do it properly and further development is needed. (mainly legend issues. The "observations" legend part is added afterwards, not inside the PlotForecastPDF() function). Note that the top-right map is not intended to be added inside the function.

I'll post in this issue when I return to this development.

Francesc