Fix node 0,0,0 being highlighted when enable_node_highlighting == false

Without this patch node 0,0,0 is highlighted when enable_node_highligting is false
There is a minor lighting issue remaining, however it seems to be related to a different bug (https://github.com/minetest/minetest/issues/1887)
Fix settings callback "call" lost on rebase
Add fontengine.cpp to Android.mk
Fix style of comment in minetest.conf.example
Add node_stone to mgv5 biomes. Remove unnecessary underwater grass hack from mgv5
Mgv7: add definable node_stone. Reduce and correct depth of biomes. Remove unnecessary grass under water hack
l_mapgen.cpp: add '#include mapgen_v5.h' because '#include mapgen_v7' is there