Updated analyze.center_box to take/return 3D array instead of 3 separate arrays.
	modified:   analyze.py
	modified:   halo.py
	modified:   hdf5.py
	modified:   multiplot.py
renamed set_viewpoint to set_view; removed centering command from set_view -- center manually BEFORE rotating.
	modified:   visualize.py
project(): load density for centering if not already loaded for plotting.
	modified:   visualize.py