feat: implement comparison skeleton

This commit lays out the general idea of how the ComparisonData struct will work. It is expandable and I'm sure we will add more to it as time goes on.

src/common/mod.rs

@@ -1,6 +1,7 @@
+mod comparison;
 mod expandable_info;
 mod form_schema;
 mod user;
-pub mod value_type;
+mod value_type;
 
-pub use self::{expandable_info::*, form_schema::*, user::*, value_type::*};
+pub use self::{comparison::*, expandable_info::*, form_schema::*, user::*, value_type::*};