Cache the initial path layer for faster path search startups.

Reinitializing the initial cell info layer for the path search took a fair bit of time. We cache this initial setup so it only has to be done each time the map size changes. A CopyValuesFrom method in CellLayer is provided which copies values between layers by just copying the internal arrays for super speed.

This speeds up InitCellInfo 10x.
Merge pull request #7108 from RoosterDragon/faster-path-init

Cache the initial path layer for faster path search startups.
implement Ordos nerve gas missiles as warheads

closes #2838
Merge pull request #6679 from Mailaender/change-owner-warhead

Implemented Deviator nerve gas missiles as warheads
Move more traits from Mods.RA to Mods.Common
Rename Util.cs to BuildingUtils.cs
Move Activities CallFunc, RemoveSelf and SimpleTeleport to Common
Move various RA-specific traits to the new folder/namespace structure
Move 'Activity' into its own namespace in OpenRA.Game.
Merge pull request #7129 from reaperrr/ra-common15

More Mods.RA/Mods.Common reorganisation
Move mission objectives and victory conditions to Mods.Common
Add plumbing for short game option
Add short game option to GUI
Adjust rules
Adjust minigames
Adjust missions
Punctuation fixes