[Refactor:RainbowGrades] first/last name to given/family name (#80)

Submitty/Submitty#10259

According to discussion made in above PR, we will be replacing
First/Last name to Given/Family name
While internally our rainbowgrades code uses first/last name as variable
(ex `getFirstName()`) changing it internally is a low priority && high
risk (needs careful review), but it will be displayed in html with
Given/Family name now.

See attached screenshot for rendering.

![스크린샷 2024-07-11 오전 7 15
38](https://github.com/Submitty/RainbowGrades/assets/123261952/268feb07-4408-4ecf-9a55-b70bda3fe502)

![스크린샷 2024-07-11 오전 7 17
13](https://github.com/Submitty/RainbowGrades/assets/123261952/52115e2d-85d0-4b3e-95cc-0bb3d5d1440d)

output.cpp

@@ -577,12 +577,12 @@ void start_table_output( bool /*for_instructor*/,
   student_data.push_back(counter); table.set(0,counter++,TableCell("ffffff","USERNAME"));
   student_data.push_back(counter); table.set(0,counter++,TableCell("ffffff","NUMERIC ID"));
   if (DISPLAY_INSTRUCTOR_NOTES || DISPLAY_FINAL_GRADE) {
-    table.set(0,counter++,TableCell("ffffff","LAST (LEGAL)"));
-    table.set(0,counter++,TableCell("ffffff","FIRST (LEGAL)"));
+    table.set(0,counter++,TableCell("ffffff","FAMILY (LEGAL)"));
+    table.set(0,counter++,TableCell("ffffff","GIVEN (LEGAL)"));
   }
   int last_name_counter=counter;
-  table.set(0,counter++,TableCell("ffffff","LAST"));
-  student_data.push_back(counter);  table.set(0,counter++,TableCell("ffffff","FIRST"));
+  table.set(0,counter++,TableCell("ffffff","FAMILY"));
+  student_data.push_back(counter);  table.set(0,counter++,TableCell("ffffff","GIVEN"));
   student_data.push_back(last_name_counter);
   student_data.push_back(counter);  table.set(0,counter++,TableCell(grey_divider));