fixed a NullReferenceException on TilesetBuilder export

closes #4506
Reduced turret range values

Reduced Guard Tower weapon range from 6 to 5
Reduced Gun Turret weapon range from 6 to 5
Reduced Sam Site weapon range from 10 to 7
Reduced Advanced Guard Tower weapon range from 8 to 6
Reduced Obelisk of Light weapon range from 8.5 to 6.5
Reduce turret vision & Increase Build Time

Guard Tower
- Reduced vision from 7 to 6
- Increased buildtime from 12s to 24s

Gun Turret
- Reduced vision from 7 to 6
- Increased buildtime from 15s to 30s

SAM Site
- Increased buildtime from 18s to 36s

Advanced Guard Tower
- Reduced vision from 9 to 7
- Increased buildtime from 24s to 48s

Obelisk of Light
- Reduced vision from 8 to 7
- Increased buildtime from 36s to 52s
Added a camera to the A10. That spawns as they attack, and is destroyed as they leave
Added INotifyKilled to AttackBomber
Merge pull request #4721 from Smilex/A10_vision

closes #4696
closes #4687
Update CHANGELOG

#4721
Merge pull request #4714 from Mailaender/tile-export-nre

Fixed a NullReferenceException on TilesetBuilder export
removed demo.mix
Merge pull request #4750 from Mailaender/demo-mix

Removed demo.mix
Adjusted AA Guns to fire their guns alternately at a high fire rate, and added contrails to their bullets.
Merge pull request #4756 from ScottNZ/aagun

AA gun polish
Merge pull request #4724 from RiderRockon/bleed

Reduced range and increased build time of static defense
Update CHANGELOG

#4724
Rebalanced Viceroids and Tiberium. PR number 4745.
Merge pull request #4745 from Iamgoofball/bleed

Changes to Tiberium and Viceroids
Update CHANGELOG

fix commit b5b98feadb1863694e31f4a60d0d0b41a141a9c1
Aircraft defence balance changes
Merge pull request #4766 from cjshmyr/balance

Aircraft defence balance changes
added a snow variation of TENT by Kilkakon

http://kilkakon.com/kocb/tent.zip