Added global flag for mod, "emex_active"

*Negyem Flu cure research now takes 2 years minimum
*Fixed possible issues where a Negyem Flu consequence could occur even after a cure was found
*Fixed possible problem where not all negative deposits relating to the Flu spread were removed upon finding a cure
*Changed weights of and time until Flu consequences
*Changed the Poisonous Atmosphere deposit to the rare category so that it appears higher up on the planet view

Initial upload! The first proper version that should be functional with the latest version of Stellaris (3.2.2 at time of writing).