Resize default_clay_brick.png from 16x17px to 16x16px, as mentioned in issue #1855

This is the maximum level of the other diamond tools and makes the
number of uses similar to them.

Only register floatland biomes if mgv7 'biomerepeat' flag is false.
Simplify floatland biomes to coniferous forest and ocean.
Make 'mgv7_floatland_level' and 'mgv7_shadow_limit' parameters global
values for mods to use to register their own floatland biomes.

Required due to the settable player collision box engine feature.
Change for MT/MTG v0.5.0 that breaks compatibility with old clients.

For axes and hoes only use one recipe that matches the appearance of the texture and in inventory.

Previous times were chosen using statistical maths, but reports suggested
this was too long.
I tested by timing an ABM acting on 100 nodes, with interval and chance equal
to the old sapling ABM.
50 at 4m59s.
99 at 24m58s.
100 at 26m58s.
So choose a grow time between 5 and 25 min for tree and bush saplings.
If 'can grow' is false at grow time the timer is reset to 5 min.

With thanks to MarkuBu for the original PR and GreenXenith for the stair models.

This allows us to preserve mgv6 ore distribution while giving us the freedom
to alter ore distribution for other mapgens.
Other mapgens are larger scale and have 3D noise tunnels which make vertical
travel easier, so ores can be deeper.
Other mapgens have registered biomes which allows us to limit ores to certain
biomes.

It is useful for protection mods to know who owns an exploding
TNT block. This allows the blocks destroyed by the TNT to be
limited to the same ones the owner could destroy without using
TNT.

TNT placed within a protected area by the area owner, and later
ignited by another player will destroy within the protected area
nodes the igniter may not otherwise be able to interact with. Any
player could significantly increase the size of an explosion by
placing more TNT in an adjacent unprotected area if the original
TNT block was placed withing 1 node of such a boundary. This
feature sounds dangerous, but we are talking about TNT. Players
should use it carefully.