Separately configurable forward/reversed funnel speeds

[vrad-exe]

Allow setting different speeds for forward and reversed funnels, like in mp_coop_tbeam_maze in the coop campaign.

[Endernice61]

This would only work if all funnels are going the same direction. Unfortunately rendering two funnels on the screen with different speeds at the same time causes flickering.

[TeamSpen210]

There is support for different speeds for the forward and reversed funnel.

[Konclan]

Added with commit 7c59e00