Next API changes

• Behavior change template
• HostAxesBase.get_aux_axes now defaults to using the same base axes class as the host axes
• plt.get_cmap and matplotlib.cm.get_cmap return a copy
• Template for deprecations
• Deprecation aliases in cbook
• AXes subclasses should override clear instead of cla
• draw_gouraud_triangle
• Development change template
• Removal change template