Alias string to cotton

Cotton plants used to drop strings, now they drop farming:cotton. Some mods (namely, throwing) still use farming:string, therefore we need farming:string to be equal farming:cotton.
Fix desert_sand_soil dropping itself, and changed the descriptions
Retain sign text when editing is aborted by <esc>
Consistently use group:stick in tool recipes

The left-handed recipes for axes were using default:stick instead of
the group:stick used by all other tool recipes.
Improve message about screwdriver control

The message to "hold shift" makes an unwarranted assumption about the
user's keybindings.  Messages from the server should refer to a key's
game function, rather than its extragame identity.
Make open trapdoor climbable

When a trapdoor is mounted upside down, to make its top surface flush
with the floor above when closed, it is necessary to have some way to
climb through the trapdoor node when it's open.  Making it climbable
like a ladder satisfies this need.  It is somewhat realistic, as a real
trapdoor can have a ladder segment mounted on one face.  When the trapdoor
is mounted in its default orientation, making the bottom surface flush
with the ceiling below when closed, the climbability when open is not
strictly necessary, but is still a convenience.
Pair door with door of any type

Mirror the setup of a door placed next to any door, not just next to
a door of the same type.  This is particularly useful where there are
multiple door types that have the same appearance, but one wants the
doors of a pair to have different behaviour in some other respect.
Rewrite TNT
Show filled buckets in creative inventory
Fix TNT init for undefined enable_tnt setting
Fix boat flying up and some tweaks