Advanced trading modifications, maintain_area modifications (#1780)

* Advanced trading modifications, maintain_area modifications

This lot of changes brings forth the following:

Sets up a "default" set of compiles that are the minimum needed for
maintain_area.sqf and custom scripts to utilize the gem based currency
that @icomrade added.

maintain_area.sqf: This will now utilize the gem based currency system.

Removed the redundant Z_Vehicle and replaced it with the Epoch built in
DZE_myVehicle

z_at_buyItems: Code tidying and optimization

z_at_checkCloseVehicle: Tidied up the code since removing Z_Vehicle
allowed us to remove some now useless code.

z_at_getVehicleItems: Removed the nearestObjects check for your vehicle
since we now do z_checkCloseVehicle on Advanced trading start up.

* Advanced trading missed redundant variables

As per description

* Advanced trading rework

We don't need to check for close vehicle anymore now for backpack money
since we've made z_vehicle redundant.

* Revert "Advanced trading rework"

This reverts commit a589bd19b9.

* Advanced trading rework

We don't need to check for close vehicle anymore now for backpack money
since we've made z_vehicle redundant.

* Advanced trading rework

More rework

* Remove single currency add/remove coins functions

at request of @ebaydayz.

SQF/dayz_code/actions/AdvancedTrading/functions/DZE_deleteTradedVehicle.sqf

@@ -38,7 +38,7 @@ if ((count _VehKey2) > 0) then {
 				};
 			};
 		};
-		_vehicle = Z_vehicle;
+		_vehicle = DZE_myVehicle;
 		if (count _this > 2 && {isNull _vehicle}) then {
 			_vehicle = _this select 2;
 		};