stabilized integration tests: use id for saving account

src/main/java/de/deadlocker8/budgetmaster/categories/CategoryController.java

@@ -90,7 +90,7 @@ public class CategoryController extends BaseController
 	public String editCategory(Model model, @PathVariable("ID") Integer ID)
 	{
 		Optional<Category> categoryOptional = categoryService.findById(ID);
-		if(!categoryOptional.isPresent())
+		if(categoryOptional.isEmpty())
 		{
 			throw new ResourceNotFoundException();
 		}

src/test/java/de/deadlocker8/budgetmaster/integration/helpers/IntegrationTestHelper.java

@@ -144,7 +144,7 @@ public class IntegrationTestHelper
 		wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("account-name")));
 		WebElement inputAccountName = driver.findElement(By.id("account-name"));
 		inputAccountName.sendKeys(accountName);
-		driver.findElement(By.tagName("button")).click();
+		driver.findElement(By.id("button-save-account")).click();
 	}
 
 	private void matchAccounts(List<String> sourceAccounts, List<String> destinationAccounts)