multi-param case: added limits and fixed status plot

[sofia-calgaro]

Limits, for plotting, were missing from the dictionary plot_info in plotting.py. Added to it as a dictionary, ie as "limits": { par1: [A1, B1], par2: [A2, B2]}. They were later included as lines in plots.

[sofia-calgaro]

Tested and found to work for:

• "variation": trueand limits!=None
• "variation": true and limits=None both for par1 and par2
• "variation": true and limits=None for par1 and limits!=None for par2 (and vice versa)

The status plots, one for each parameter, are simply added to the pdf already containing the par1 vs par2 plots.