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

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

Move NodeMetadata prototype containers to content_nodemeta.cpp to fix them not being filled correctly on some systems and compilers

Switch more stuff to use the logging thing and fix segfault on player leave from server as introduced in a previous switch-to-logging commit

* I didn't understand that expression last fix and now the furnace would burn fuel
even when it had no source item.

This one contains these changes from main c55:
* Adds a function to check if there is room for a specific item
* Using that, you can now pick up rats if you have a full inventory and a not full rat stack
* Furnace would cook only 1 item if that item used the last available result slot, now it will continue
* Furnace will say it's overloaded
* Furnace won't wait until the next step to start on the next item
 - This caused small fuels to cook slower than meant to
 - Also caused furnaces to say they were out of fuel after finishing the last fuel item

Moved some mapnode content stuff from mapnode.{h,cpp} and digging property stuff from material.cpp to content_mapnode.{h,cpp}

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

--HG--
rename : data/tool_stpick.png => data/tool_stonepick.png
rename : data/tool_wpick.png => data/tool_woodpick.png