Merge branch 'bones_was_here/q3compat' into 'master'

Merge branch bones_was_here/q3compat

Closes #2465

See merge request xonotic/xonotic-data.pk3dir!849

diff --cc qcsrc/common/mutators/mutator/powerups/powerup/invisibility.qh
Simple merge

diff --cc qcsrc/common/mutators/mutator/powerups/powerup/speed.qh
Simple merge

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

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

diff --cc xonotic-server.cfg
Simple merge