Fix errors in shape documentation

There are 26, not 25 shapes (shape 0 was not shown). Only symbols 21
through 25 have a fill option; 19 and 20 do not.
Improved graphic for shapes catalog

Revamped the graphic for showing the different shapes (0-25) utilizing
facet_wrap instead of staggering along the axes. Also using theme to
get rid of unnecessary elements, but retainging the grid lines that show
exactly where the points are centered. Changed the fill from black to
lightblue and made the symbols bigger.
Move scale_shape_identity into s
Commit corresponding Rd file
Merge remote-tracking branch 'origin/doc/shape' into doc/aesthetics

Conflicts:
	R/aes-linetype-size-shape.r
	man/aes_linetype_size_shape.Rd

Better representation of all shapes.