feat: begin implementation of "sub tabs"

src/pages/student/mod.rs

@@ -1,7 +1,9 @@
 mod shell;
 mod home_page;
 mod demographics_page;
+mod additional_page;
 
 pub use shell::*;
 pub use home_page::*;
-pub use demographics_page::*;
+pub use demographics_page::*;
+pub use additional_page::*;