[Character] Convert Load/Update of Character Alternate Currencies to Repositories (#3856)

- Convert `LoadAltCurrencyValues` and `UpdateAltCurrencyValue` to repositories.
- Cleanup some other code and logic as well.
- Add `AlternateCurrencyMode` namespace for `AltCurrencyPopulate_Struct` opcode magic numbers.

common/eq_constants.h

@@ -727,6 +727,11 @@ namespace BuffEffectType {
 	constexpr uint8 InverseBuff = 4;
 }
 
+namespace AlternateCurrencyMode {
+	constexpr uint32 Update   = 7;
+	constexpr uint32 Populate = 8;
+}
+
 typedef enum {
 	FilterNone = 0,
 	FilterGuildChat = 1,		//0=hide, 1=show