Inconsistent variables/modules names in plotmon and instrument monitor

We have adopted snake_case and CamelCase for naming the variables.

Several variables in the plotmon and instrument monitor are not consistent with this and need to be changed before a v1.0:

• quantify.visualization.pyqt_plotmon -> plot_monintor_pyqt
• quantify.visualization.pyqt_plotmon.PlotMonitor_pyqt -> PlotMonitorPyQt
• quantify.visualization.pyqt_plotmon.PlotMonitor_pyqt.setGeometry_main -> set_geometry_main
• quantify.visualization.pyqt_plotmon.PlotMonitor_pyqt.setGeometry_secondary -> set_geometry_secondary
• quantify.visualization.pyqt_plotmon.PlotMonitor_pyqt.main_QtPlot -> main_plot
• quantify.visualization.pyqt_plotmon.PlotMonitor_pyqt.secondary_QtPlot -> secondary_plot
• quantify_core.visualization.instrument_monitor -> instrument_monitor_pyqt
• quantify_core.visualization.instrument_monitor.setGeometry -> set_geometry

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