More Great Artists

Adds 28 new Great Artists across most Eras - I'm working on adding at least 7 more (so that there's 5 per Era, excluding Ancient). I had planned on making the new buildings and changes to the existing buildings optional via 'Advanced Setup' but haven't been able to get the criteria functionality to work reliably. Hopefully I'll be able to add this in soon. Additional changes and additions include the following, check out the Civilopedia for more details on everything. Passive Effect All Great Artists now have a Passive Effect -> +1 Culture to the tile they are currently in (they have to be standing in the tile for a full turn for it to take effect). Note that like all tile yields, the tile needs to be worked by the city in order for it to be useful. Now all those Great Writers standing around actually contribute something. New Building - National Gallery A new buliding that can be built in a theater district once you have the Nationalism civic. There can be only one - in each civ. This has 3 Great Work of Art slots and is themed by unique person. New Building - Statue Adds a new buliding that can be built in a city center once you have the Early Empire civic. +2 Culture and +1 Great Artist Point. You can only build 3 in your Empire, and if you build one in your capital it will add a Great Work slot to your palace. New Building - Art Studio Adds a new buliding that can be built in a theater district you have the Medieval Faires civic. +2 Culture and +1 Great Artist Point. 1