Shadily clean up NDT_RAILLIKE to surely differ from the few leftover non-LGPLv2 parts from the standpoint of copyright law.

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

Fix flowing liquid spacing; water and lava next to each other will glitch a bit but it isn't as bad as this was

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.

Completely rewrote the liquid transformation. The algorithm now exclusively modifies the current node in one iteration. Another change is that MapNode.param2 now stores a bit that tells other nodes if a flowing liquid node flows downwards. This is accomplished by two masks on param2 for the "flow down" bit and the "liquid level" bits.

This will be the base of future improvements to the liquid flow. However, in the current state flowing liquid does not always disappear when cut off its source. Be aware that this branch is work in progress.