[with patch; positive review] 3d and 2d graphics -- some unification

[was]

Make it so that the following sort of thing works:

sage: sphere() + plot(sin(x), (x,0,10))
sage: plot(sin(x), (x,0,10)).graphic3d()

and

sage: plot(sin(x), (x,0,10)).show(viewer='jmol')

In each case the plot would be rendered using 3d primitives instead of 2d primitives, when possible -- primitives that aren't implemented in 3d would degrade or be removed. Basically make a way of coercing 2d plots into the world of 3d plots.

This would make it possible to view whole arrays, groups, whatever of 2d plots all organized in some spatial way in 3d, and also to zoom in very close, etc., on 2d plots.

[robertwb]

I've implemented turning most 2d primitives into 3d primitives, e.g.

sage: sphere(aspect_ratio=[1,1,1]) + plot(sin(x), 0, 10)
sage: sum([plot(z*sin(x), 0, 10).plot3d(z) for z in range(10)])

[was]

AWESOME!!

Just playing around

sage: var('x y'); p1 = parametric_plot3d((x,y,0), (x,-2,2), (y,-2,2), color='red', opacity=0.5)
(x, y)
sage: p2 = plot(sin(x),(-2,2)).plot3d().translate(0,0,0.1)
sage: p1 + p2 + sphere((0,0,1),0.01) + polygon([(0,0), (0,1), (1,2), (2,0)]).plot3d().translate((0,0,-0.1)) + sphere((0,0,-1),0.1)

[mabshoff]

Merged in Sage 2.10.1.alpha0