Node placement / mineral / serialization / iron freq / node_dig callback

- 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.

src/servermain.cpp

@@ -68,7 +68,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "porting.h"
 #include "materials.h"
 #include "config.h"
-#include "mineral.h"
 #include "filesys.h"
 #include "defaultsettings.h"
 #include "settings.h"
@@ -301,10 +300,6 @@ int main(int argc, char *argv[])
 	srand(time(0));
 	mysrand(time(0));
 
-	// Initialize stuff
-	
-	init_mineral();
-
 	/*
 		Run unit tests
 	*/