Codechange: Split CT_INVALID into CT_INVALID and INVALID_CARGO.

INVALID_CARGO is a CargoID and should be used for most purposes in game.
CT_INVALID is a CargoType used for defining default properties.

Add: deity mode enforcement checks to functions with command or company access

Command functions are those that call ScriptObject::Command, and functions
with company access are any that call ScriptObject::GetCompany. This is a bit
over-protective, but having the check everywhere makes it easier to validate
that no check is missing automatically instead of by review.

Codechange: use GSCompanyMode::IsValid, IsDeity, and the precondition helpers

Direct 1:1 replacements in the code, and comments now refer to either
GSCompanyMode::IsValid or GSCompanyMode::IsDeity instead of several variations
on "company mode active" or "no company mode active".