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.