-TryDiscardFunction in battlescene;
-Created a party discard mode button;
-Updated Transfer button in modifier-select-ui-handler to Manage items;
-Created tests for the discard function in test/ui;
-Added images for the new discard and transfer buttons to loading-scene;
-Created placeholder messages for discard feature in party-ui-handler;
Co-authored-by: Tiago Rodrigues <tiago.n.rodrigues@tecnico.ulisboa.pt>
