Feature: tune_monitor selection in tune_correction

@GamelinAl, @kparasch, Ivan Morozov and Julian Gethmann
a default should be determined for betatron tune monitor, with option to select an other tune monitor if available in the config file

tune_monitor = control_mode.get_betatron_tune_monitor("BETATRON_TUNE")

Also, tune_correction should return the quadrupole and tune monitor used by the correction