Add bunch to bunch monitoring of the CavityMonitor

Add a dict_dtype optional parameter to Monitor.monitor_init to allow to choose the dtype to use to save the data.
Improve CavityMonitor to allow for saving beam and cavity phasor for all bunches
Add a plot_cavitydata function
Fix a bug on CavityResonator.track -> nturn += 1 at correct time
Change CavityResonator.track to allow for monitoring the cavity/beam phasor at each bunch