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

inventorycube: use all three specified textures; also moved mesh creation / modification functions to mesh.cpp; in lua, inventorycube is now called minetest.inventorycube

Make camera.cpp Irrlicht 1.8-compatible by calling ITexture::lock differently depending on the irrlicht version.

Fix single-frame lag in camera yaw/pitch, tune view bobbing and add wielded tool movement when walking and tweak stuff a bit