Pre-FTL City Sets & Rooms (& Flags)

Adds the Pre-FTL city sets & rooms (& flags) to the empire customization menu as selectable options. Generated empires should not be able to utilize them. Ecumenopolis cities are included albeit not tested, but from what I observed from the vanilla game's files & contents it should work. Obviously all credits of the visuals belong to Paradox Interactive and the relevant artists. I only photobashed the ecumenopolis variants with the existing game art. This is my first mod so if something doesn't work let me know here and I'll do my best to fix it, time and circumstances permitting. It is also important to note that this mod is not achievement compatible. Due to the way that I had to set it up the game views it as a gameplay alteration. It is a result of ensuring that random empires cannot use these customizations and that the city sets make proper use of the ecumenopolis variants. Nothing to be done about it, sadly.