Added a global variable SHOTPLOTS to the plot module to show plots directly in Console/Notebook cells

Added a global variable SHOTPLOTS to the plot module. If blond.plots.plot.SHOWPLOTS = True, then the plots that are normally saved are instead directly displayed in the console. Additionally, all plot output besides the plot of the longitudinal phase space distribution now uses matplotlibs tight layout, meaning that the plots should be automatically scaled such that all elements are visible fully. However, for this to happen, the explicit axis definitions have been removed, so plots will look slightly different than before.