Add is_ground_content setting to grass_1, apple, and dry shrubs
Explicitly set values of is_ground_content

Counterpart commit to minetest 9a927476
Add waving property for leaves and plants.
Fix player skin changing code.
Use minetest.swap_node instead of hacky_swap_node
Rework screwdriver and add protection support
Check for area protection in buckets
Shorten lines in bucket and support nil placers
Allow changing screwdriver mode when pointing at a protected node
Add protection support to signs
Prevent bucket from replacing unloaded nodes