Create class `CalibrationPlot`

Create a new class CalibrationPlot to store all parameters related to calibration plotting.

An instance of CalibrationPlot should be created when reading a YAML file. For example

simulation:

  mode: calibration

  calibration:
    ...

  outputs:
    output_folder:        'examples/CTI/output'
    calibration_plot:                    <--+
      champions_plot:                       |
        plot_args:                          |
          yscale: 'log'                     |
      population_plot:                      |
        columns: [2, 4]                     |
        plot_args:                          |-- instance of `CalibrationPlot`
          xscale: 'log'                     |
          yscale: 'log'                     |
          title: 'trap specie #1'           |
          xlabel: 'release time (s)'        |
          ylabel: 'density (cm$^{-3}$)'  <--+

  ...

Class CalibrationPlot must be used when instantiation an Outputs class with parameter 'calibration_plot'.