[Commands] Add #setaltcurrency Command. (#1850)

* [Commands] Add #setaltcurrency Command.
- Add #setaltcurrency [Currency ID] [Amount] command to allow you to set a specific alternate currency to a value.
- Add Zone::GetCurrencyID() and Zone::GetCurrencyItemID() helper methods.
- Cleanup loops through zone->AlternateCurrencies.
- Utilize helper methods where necessary.
- Convert old methods parameters and return values from int to uint32 where necessary.

* Typo.

zone/CMakeLists.txt

@@ -488,6 +488,7 @@ SET(gm_commands
     gm_commands/set_adventure_points.cpp
     gm_commands/setaapts.cpp
     gm_commands/setaaxp.cpp
+    gm_commands/setaltcurrency.cpp
     gm_commands/setanim.cpp
     gm_commands/setcrystals.cpp
     gm_commands/setendurance.cpp