Add a new civilization to the game about 0ad

[luumu]

Faction: Cherusci
Desc: Combines the Gauls and Britons civ bonus (celt structures) and the Spartans population malus (though split to a separate bonus for a greater malus -20% max pop) and female citizens can build walls. Uses mix Briton/Gaul unit graphics(brit cav, gaul inf).
Special tech: +10% movement speed tech available in the barracks building at town phase (Custom tech “Schlacht im Teutoburger wald”) note: this may or may not be overpowered, haven’t played enough to know yet.
Hero: Arminius (Uses the model and textures of the Gaul hero Brennus). Gives a bonus to attack strength, attack range, and capture attack.
Visual changes: Custom emblem using the following copyright-free image: https://publicdomainvectors.org/en/free-clipart/Eagle-with-German-flag-vector/27441.html
Custom rally point banner (recolor of the Ptolemies banner). Art/units folder was also created for the nation, although it still uses Gaul/Briton assets, this was done so that if custom textures and meshes were to be made for the nation the work to implement them would be less. All units and buildings have new names for the nation, though they are in modern German whereas historically the names would be proto-Germanic.