several fixes

[sofia-calgaro]

• plotting.plot_per_string() is back to its original form (all strings in one figure) -> you can still obtain one string per figure starting from an external code, you just subselect the dataframe section corresponding to the string of interest instead of passing the full dataframe as input
• fixed if statements for resampled option in plotting.py
• removed "if pulser" in plotting.plot_per_string() (wrong copy+paste): the function perfectly works also for one channel only, as it is the pulser
• fixed colours when selecting different resampled options
• fixed data_analysis.data into data_analysis (dataframe object) in all functions of plotting.py but make_subsystem_plots() (left some freedom there) and inside status_plot.py