Rogue's Civarium - Sumer (Antiquity) 0.13

Thanks @egn for the stellar feedback
- Variety of balancing tweaks (with Abul-Urudu in particular)
- Bronze should now properly be given with the construction of the Abul-Urudu
- Some constructible have been moved around
- The Ziggurat now properly receives bonus from floodplains (I think, please test)
- Suku Rations now only benefits from navigable rivers, but gives more food
- The Abul-Urudu is slightly nerfed
- Added an icon to the civics tree

Fixed some text, tweaked some balance.

Thanks to Toryjang for the bug report
Writing now should only unlock for Sumer, instead of for all civilizations when the mod is enabled.

Hotfix: Localization text for unlocking the Abbasids by playing as Sumer is now corrected.