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

Reduce EnvRef:set_node() time tenfold by postponing the dayNightDiff update until it is actually needed

- 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.

Collected and moved existing camera infrastructure from game.cpp to camera.cpp and camera.h. Introduced configuration settings 'fov' which chooses the camera's (vertical) field of view and 'view_bobbing' which currently does nothing. Other code refactored to not expect the FOV to be a build time constant.

Removed unused camera_position and camera_direction fields from Client. Moved ClientEnvironment::drawPostFx to ClientMap::renderPostFx -- this will make the camera management classes easier to write, as ClientMap already knows the camera position but ClientEnvironment doesn't and has to be told about it. This also eliminates the need for Client::getEnv(). Made the post effect color a content feature defined in content_mapnode.h.

* The map will reside in world/map.sqlite
* It will load from the sectors folder but will not save there

Fixed objects being sometimes not able to be stored statically in a block when block has been unloaded

New map generator added (and SQLite, messed up the commits at that time...) (import from temporary git repo)

Reduced server CPU usage on NodeMetadata step()s. Also furnace now cooks while no players are near it.