Explosive Oil Derricks
Changed some tiles types
Merge pull request #5930 from MustaphaTR/ra-oil-explode

RA - Explosive Oil Derricks
Added some trait [Desc()]s.
Merge pull request #5946 from Phrohdoh/MoreTraitDocs

Added some trait [Desc()]s.
Merge pull request #5932 from MustaphaTR/d2k-only-inf-fix

D2K - Fixed some tiles should be only infantry
Hijacker again buildable by soviets
Restored production queue current item checks

Fixes regression #5948 where you could freely build any building by
canceling the production before deploying by restoring the currentItem
checks in the PlaceBuilding order to ensure that the production is still
valid.
Merge pull request #5954 from abcdefg30/fixhijacker

Made Hijacker buildable by soviets
Merge pull request #5955 from Squiggles211/production_cancel_fix

Restored PlaceBuilding order's ProductionQueue checks.
Add support for mission objectives
Move trigger lists into a dictionary for easier access and enumeration
Add mission objectives to Lua interface
Make CheckboxWidget honour GetText()
Add a mission objectives GUI panel
Make scripted maps at least partially objective-aware