Fix visual_scale for plantlike nodes (again)

fixes #1989

move the plant to the bottom of its node properly, without affecting its scale.  See isue #1989
Change TileSpec::frames to be std::vector not std::map

Signed-off-by: Craig Robbins <kde.psych@gmail.com>
Re-add hacky fix for underwater grass, to fix mgv7 user's biomes
lua_api.txt: improve noise documentation. Remove previous eased 3D noise format example