add dto, refactor names, update controllers

src/main/java/com/faf223/expensetrackerfaf/dto/IncomeCreationDTO.java

@@ -0,0 +1,12 @@
+package com.faf223.expensetrackerfaf.dto;
+
+import com.faf223.expensetrackerfaf.model.User;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+@Data
+@AllArgsConstructor
+public class IncomeCreationDTO {
+    private long incomeId;
+    private User userDTO;
+}