Merge branch 'z411/powerups_dropondeath' into 'master'

Merge branch z411/powerups_dropondeath (improves on Mario's implementation)

See merge request xonotic/xonotic-data.pk3dir!943

diff --cc qcsrc/server/items/items.qc
Simple merge

diff --cc qcsrc/server/items/items.qh
Simple merge

diff --cc qcsrc/server/items/spawning.qc
Simple merge

diff --cc qcsrc/server/world.qc
Simple merge

diff --cc xonotic-server.cfg
Simple merge