Revert "Convert axes plotting functions to staticmethods."
This reverts commit 55daa0e98aa4cd392880c7664b4fcc9aabb372d2.
	modified:   pyGadget/plotting.py
New plotting module.  Goal is to make it more flexible - handle multiple snapshos in one figure.
	new file:   multiplot.py
Added multiplot to __init__
New module halo.py for new Halo class (wrapper around an SQL database
containing derived halo properties).
Moved relevant functions from analyze.py to halo.py
	modified:   __init__.py
	modified:   analyze.py
	new file:   halo.py
Enabled population of database.
	modified:   halo.py
Basic working halo class.
	modified:   halo.py
Added method for plotting gas temp vs radius.
	modified:   multiplot.py
Corrected radial-temp xlims.
	modified:   multiplot.py
find_center() no longer requires gas density to function. (more robust)
Can also specify center to re-arrang particles against.
	modified:   analyze.py
New method calculate_spherical_coords().
Also updated get_coords to have option of returning spherical coordinates.
	modified:   hdf5.py
Split analyze.find_center() into two more sensible functions.
	modified:   analyze.py
	modified:   halo.py
	modified:   hdf5.py
	modified:   multiplot.py
	modified:   visualize.py
Updated snapshot plot functions to specify centering algorithm.
	modified:   snapshot.py
Bugfix in calculate_spherical_coords()
	modified:   hdf5.py
Added functions for transforming between cartesian & spherical coordinates.
	modified:   analyze.py
Added new functions for rotating the view.
	modified:   visualize.py
New plotting function for rotating about a cardinal axis.
	modified:   snapshot.py
Fixed bug in z-axis rotation.
	modified:   visualize.py
updated rotation plot function.
	modified:   snapshot.py
Fixed viewing angle bug.
	modified:   snapshot.py
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