Rebase test_plot on master
plot_phasespacedata -> only "particles" dataset is plotted
plot_phasespacedata -> mandatory arguments

- total_size and save_every input parameters have been removed.
- only_alive option function has been changed
- Some small corrections on scaling of delta, bunch_charge, bunch_current

- "plot_bunchdata" and "plot_phasespacedata" have been separated from particles module.
- Input prompt has been removed from the code.
- Plotting method for variables in Beam object such as "bunch_current" and "bunch_charge" with respect to bunch number has been added.
- Only alive particles plotting option has been added.