fixed K events parameter

[sofia-calgaro]

Simplified the "K events" plotting: now, if you want to plot only those energy events that lie in [1430,1575] keV, you have to build the following subsystem entry:

"subsystems": {       
      "geds": {
          "K events":{
              "parameters": "K_events",
              "event_type": "K_lines",
              "plot_structure": "per string",
              "plot_style" : "scatter"
          }
      }
  }

"cuts": "K lines" is no more needed as it was before (indeed, since we are already specifying with the parameters entry that we want to look at K events, it would be redundant to add also that cut).

The cut over K lines entries is still an option for plotting other parameters in correspondence of K entries. However, it still does not work because in the dataframe the energy column is missing (eg. if we want to plot the baseline in correspondence of K entries, we cannot do it at the moment because the code does not know that it also has to load an energy column, which is needed for applying the energy cut). This problem was already there, and it seems it can be solved by simply loading the additional energy column if "cuts": "K lines" is present for a given parameter.