Merge tag 'v0.31.0' into debian

Alpha 31 release
Update changelog.
Merge branch 'master' into debian
Update changelog.
Merge branch 'master' into debian
Increase particle system limits.
Add cg_spawnEffects to disable spawn colorgrading since OSX doesn't like it
Fix error message
Move build timer under momentum bar
Fixes #455
Revert "Add a check to avoid sending sync messages while handling async messages"

This reverts commit 1ca7b09bc22b95920768d9b946043a6d8e70aa90.
Causes crash if any player disconnects
Clear the tutorial text when the cvar is disabled
Fixes #457
Replace std::map with std::unordered_map in PropertyMap
Restore previous weapon HUD upon vid_restart
Adding /playSound /playMusic /stopMusic command
Merge pull request #463 from mwestphal/master

Adding /playSound /playMusic /stopMusic command
Fix id of the 'Resume Action' button
Fixes #464
Remove feature test macros from qcommon.h
Detect a missing opusfile at configure time. Fixes #467.
Implement soft particle shader.

The new shader keyword depthFade specifies the virtual "thickness" of
the sprite.
Add depthFade to the acid tube acid shader