Fixed a problem with 2D projections

The TH1D histogram which is used to store X and Y projections was
never initialized. This was causing the program to crash when the
project command was used. Included initialization of this histogram.

Included new methods in Plotter1D and Plotter2D to set the bins and
limits of external histograms to that of the internal one (SetHist).
This makes it easier to make projections along the X or Y axes.

Also added two functions called Zero1D and Zero2D which will zero
the contents of 1D and 2D histograms respectively.