Tiny Rock final

* Rebuilt gamemode logic using VScript; the map uses the real Arena Mode gamemode logic along with the existing Payload Race logic (thanks to Leezo for setting all this up for me)
* Map prefix is now arena_ rather than aplr_
* Minor clipping tweaks

This version uses that hot new VScript magic to finally include TF2's built-in Arena Mode game logic along with the standard Payload Race game logic.

I'm uploading this as a "test" version to make sure it works properly on a full server.

Huge thanks to @leezo for doing all the VScripting and logic setup!

* Hopefully fixed rounds not ending properly when somebody joins mid-round
* Fixed a visual issue I noticed literally hours after I posted the original "final" version

Barring any glaring issues, I'm declaring this final.

* Removed mid-round spawns, players spawning mid-round now instantly die outside the playspace (but not in the ravine this time)
* Fixed players spawning in the mid-round kill room before round start
* Misc clipping and visual fixes

* Fixed some unintentional asymmetry
* Disabled collision on some small objects in the playspace
* Fixed an unintended perch point
* Minor visual tweaks

* Further optimisation
* Clipped off a spot I forgot to clip off
* Fixed a spot in the deathpit where you could stand and not die
* Lanterns are darker
* Various visual fixes
* Clipping tweaks

* Map now has clip brushes and brush entities again
* Updated briefing photos

* Some visual tweaks I forgot about

* 3D skybox!
* Soundscapes and other environment sounds!
* Actual briefing photos!
* Optimisation pass
* Updated announcer lines:
** Removed "Killstreak" lines
** "First Blood" can now trigger the "Fast" and "Slow" variants as well as standard
** Added "Flawless Victory" and "Flawless Defeat" lines
** Added "Last Man Standing" lines (thanks to Leezo for doing the map logic on this)
* Added more spectator cameras
* Changed an ammo pack from medium to large
* Widened the uphill slopes on each side of the middle bridge
* A whole bunch of detail tweaks and fixes
* Fixed "static prop with no vphysics model" errors

* Mid-round spawn rooms now kill you (after a delay)
* (Hopefully) fixed a rare bug in which the cart would not fall into the hole when captured
* Minor visual tweaks