A new arena map in 2018 for urt: ut4_octo_arena_b4

UPDATE 2018: after =0g=babbler corrected object/texture alignments in January 2016, I was a lazy *ss in mapping. So now I finally decided to fix and finalize this simple map. The map idea comes from an ancient Unreal Tournament 2004 octagonal-shaped arena map.
This map is maybe unfair for UrbanTerror team games, but has fully equal spawn places for the 12 FFA players (matches etc).
I needed to fix the edges of concrete covers, because there were a see-through-glitch.
=0g=babbler fixed the geometry of the roof still about 3 years ago.

I tested the map on my server and it ran flawless with 3 gamers and 3 bots. However I don't think it would be big/fair enough for 12+ players.

Updates in this b4 version:
- pillar in the middle for covering/holding the roof,
- fixed the glitch of the concrete covers,
- more hint areas for better performance/fps,
- direct safe spawn exits on the arena gallery to avoid main exit blocking (nadespamming),
- sentry to prevent flag hide in the spawn area,
- bot clips over the water,
- arena objects are different to pass the needs of different gametypes.

Have fun!