Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors

- Node placement code moved to Lua
- Mineral system removed (added default:stone_with_coal and default:stone_with_iron).
- MapBlock and MapNode serialization updated.
- Mapgen: Frequency of iron increased.
- node_dig callback and related changes.

The huge item definition and item namespace unification patch (itemdef), see http://c55.me/minetest/wiki/doku.php?id=changes:itemdef

Make fence post selection box smaller and create code to allow node placement to the side of a static box

Adding (most) of the sapling functionality. It has yet to work, since MEET_OTHER was not implemented at the time of this commit. Hopefully it will work when merged with celeron's latest.