Carthage has three nice-looking apartment blocks:
{F1790042, width=500}
They're already used in a few mods and some people would really like to seem the buildable by default.
This patch:
* makes the cart apartment independent from the cart house;
* makes the apartment buildable in the town phase;
* makes the apartment a bit stronger, most notably with 20 population, instead of 15.
As a consequence:
```
cart house , cart apartment
wood : 150 , 200
stone : , 50
time : 50 , 75
population : 10 , 15
garrison : 6 , 12
health : 1200 , 1800
capture points: 300 , 600
```
Initial patch by @borg-, redone and expanded by @Nescio.
Icon by @Stan, to be added later.