Add "new" JAMP engine functionality for OpenJK support

[thecybermind]

JAMP in OpenJK works currently using the "legacy" system, and can load "legacy" mods.

Need to handle being loaded with the new system, but also be able to load "legacy" mods.

The new system is just a GetGameAPI format, but called "GetModuleAPI", and uses the same functions as the legacy system, so the enums are already defined.

Need to adjust mod.cpp to fallback to attempting dllEntry loading if GetGameAPI fails. Also, check "GetModuleAPI" first if "GetGameAPI" isn't found.

Finally, game_jamp.cpp needs to add a JAMP_GetGameAPI handler along with game_export_t/game_import_t structs like other GGA games.