updated menuItemExisting to display folder icon instead of plus icon

src/main/resources/fxml/vault_list.fxml

@@ -42,7 +42,7 @@
 						</MenuItem>
 						<MenuItem styleClass="add-vault-menu-item" text="%main.vaultlist.addVaultBtn.menuItemExisting" onAction="#didClickAddExistingVault" >
 							<graphic>
-								<FontAwesome5IconView glyph="PLUS" textAlignment="CENTER" wrappingWidth="14" />
+								<FontAwesome5IconView glyph="FOLDER_OPEN" textAlignment="CENTER" wrappingWidth="14" />
 							</graphic>
 						</MenuItem>
 					</items>