The purpose of this is to allow mods to be able to interact (e.g. fill up)
an empty bucket when it is used to punch a node that's not a liquid source
or when punching a custom entity (e.g. milking a cow).

River water needs to be 'liquid_renewable = false' to avoid a mess caused by
spreading of sources, however picking it up with a bucket then creates
a hole in the river. Allow a 'force-renew' of the source node if it has a
source neighbour.

* Unused variables
* Unused values (assigned to variables, but overwritten before use)
* Defining already defined variables instead of reassigning to them.

- Placing liquid inside a protected area no longer returns an empty bucket
- Remove on_place function, tidy up code, return proper itemstack
- Shorten code (changes from HybridDog/patch-35)

Add groups to registration and use water_bucket group

This reverts commit 79856c91.

-> Empty bucket