Implement support of q3 haste

Closes #2228 (closed)

Done:

• support count field of item_haste
• do not set STAT(BUFFS) = 0 when player spawns (fixes spawn trigger which gives item_haste)
• support item_haste in target_give_init at quake3 compat code
• change only sv_maxspeed and sv_maxairspeed
• notify players when someone loses item_haste by a trigger (perhaps not needed?)
• added a cvar to toggle between Q3 haste mode and Xonotic Speed mode
• addedd a cvar to disable buff shield time (hardcoded to 0.5)
• added defrag buffs config and exec it at physicsXDF.cfg
• verified that players can't acquire buffs by spectating another player with buff and then spawning
• disabled buff picked/lost console notifications for other players, cause they are useless in CTS and just spams the console
• added sounds for when the buff is given by a trigger
• I can't reproduce unlimited buff time bug when the buff is picked instantly after the spwan

Possible improvements (I don't think they should block merging of this, perhaps worth opening another issue?):

• do not display frozen 99 in the hud powerup panel if buff timer is >99?

Notes:

• The code is running on "Relaxed Running" defrag server. I'll leave WIP on this MR for a week so we can test and reveal if there are more bugs.