Don't clear buying list on category switch + AdvTrade fixes

The buying list now acts like a shopping cart. It is no longer cleared
when switching between categories or containers. Closing the dialog or
switching to sell mode still clears it.

Also fixed:
- Filter button in sell mode
- Bug where filtering sellable list readded items already moved to
selling list
- Visual price display not clearing when remove all button is used on
buying list
- Gear container picture showing rank instead of portrait in buy mode
- Dialog is no longer closed when trying to sell zero items
- LbCurSel is now reset when the buyable list is cleared
- Category is no longer opened onLbSelChanged. Instead you need to
double click or use the "View" button, so the arrow keys can be used for
selecting too.

SQF/dayz_code/actions/AdvancedTrading/init.sqf

@@ -11,7 +11,7 @@ if(DZE_ActionInProgress) exitWith { localize "str_player_actionslimit" call dayz
 if(isNil "Z_AdvancedTradingInit")then{
 
 	//#include "config.sqf"; // Moved to dayz_code/configVariables.sqf
-	#include "\z\addons\dayz_code\actions\AdvancedTrading\functions\defines.sqf";
+	#include "\z\addons\dayz_code\actions\AdvancedTrading\functions\defines.hpp"
 
 	/* Configs that needs to be defined but not changed in config file */
 
@@ -106,6 +106,8 @@ if(isNil "Z_AdvancedTradingInit")then{
 
 Z_Selling = true; // Always start menu in buy mode (flipped in z_at_changeBuySell.sqf on startup)
 Z_CategoryView = true; // Always start in category view
+Z_BuyingArray = [];
+Z_ResetContainer = true;
 createDialog "AdvancedTrading";
 
 (findDisplay Z_AT_DIALOGWINDOW displayCtrl Z_AT_REMOVESELLITEMBUTTON) ctrlSetText " < ";