implemented amounts in gui

gui/ui/state.slint

@@ -1,6 +1,7 @@
 export struct SItem {
     name: string,
     checked: bool,
+    amount: int,
 }
 
 export global State {
@@ -13,6 +14,8 @@ export global State {
     callback add-to-list(string);
     callback check-item(string);
     callback delete-checked();
+    callback inc-amount(string);
+    callback dec-amount(string);
     in-out property <string> server-address;
     callback set-server-address(string);
     set-server-address(address) => {