Add groups to registration and use water_bucket group

This change word-wraps text when reading a book.

Uses group “connect_to_raillike”

Improved flowers' registration system - Specific nodeboxes, - Color groups - All datas were put into a table then unpacked for add_simple_flower

Used value: 2

Copy pos before giving it to on_blast because it can modify it; also remove a debug print that had nothing to do here

Implemented nodes:
- Steel Door: Ignores explosion
- Locked Chest: Ignores explosion
- Fire: Ignores explosion
- TNT: Starts burning
- Burning TNT: Explodes immediately
- Gunpowder: Starts burning
- Burning Gunpowder: Ignores explosion

Default/mapgen: Add mapgen aliases for sandstone brick and sandstone brick stair, to enable sandstone dungeons

dont grow cactus on a lying one

use minetest.get_node 2 times less

do a bit what ShadowNinja wrote

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return true if the plant is set