Add more non-combat units (music bands, merchants, explorers, etc)

To broaden the range of game mechanics, it'd be worth to indroduce more types of non-combat units to represent achievments of humankind:

- entertainment units - music bands, circus performers, sport players - units who, in thier own or foreign territories gain cultural influence, stability or money;

- merchant units - units capable of exploiting other player's resources and building special districts (outposts, guilds, corporation towers);

- world explorer units - botanists, field researchers, conquistadors, archaeologists - units that discover 'wonders' like neolithic tribes that gives additional bonuses from given domain (science points, money, etc.) with optional short pop-up events (like archaeologists in Stellaris).