Modify default grasses rather than entirely re-defining them

Also, move "waving = 1" property for grasses/shrubs over to default/nodes.lua
and put all instances of this property right under the drawtype, since they
are directly related and depend on the above.
Bugfix 204 -- adjusted cobblestone to stair ratio

Stair recipe now outputs six stairs rather than four.
Merge branch 'Bugfix204_stairs_recipe' of https://github.com/JStation/minetest_game into hversion
Merge branch 'waving_stuff' of https://github.com/VanessaE/minetest_game into hversion