Simple MVM Revive Marker v3

Moved revive marker to its own class to allow for easy extending and overwriting of the default script. This does make the initial setup a tiny bit more complicated.
Added an extra optional parameter to spawnReviveMarker which lets you set the amount of health is needed to revive a player (alongside more flexibility, this also allows you to make sure the health doesn't get too high, for gamemodes with long rounds)

Fixed players respawning while being revived. The way this is done is a bit hack-y since the game normally handles this, but that unfortunately doesn't work when the revive markers are spawned via vscript. If you get any weird things happening to players with this script (usually around the player being "alive" or "dead"), please tell me!