Docu update multiplot
- removed ussage of pandas/matplotlib in the documentations and replaced it with calls to
saqc.SaQC.plot
- added seperate legend for flags and data
- fixed overlapping xtick labels issue
- added more finegrained control of line appearance for multiplots
- changed default plot color in case of sinle variable plots to black (transparency=80%)
Edited by Peter Lünenschloß