TFTD Vanilla/DOS - Magnetic Navigation fix

Simple small mod that requires you to interrogate an Alien Navigator before you can research Magnetic Navigation. This is similar to the behavior of DOS versions of TFTD. I feel this is required because without the prerequisite you can get the Transmission Resolver super early-game, when it's supposed to be a mid-game structure.

This is one of several small mods I'm publishing to make OpenXCom/TFTD behave more like the Vanilla/DOS TFTD experience.