adding a new core module

This module will hold all the core mechanincs so that we can abstract
things further and allow for a better design of the main system. This
gives the freedom of moving the ui further from the logic and allows
for changing the ui in the future.

src/rust/core/service_items.rs

@@ -0,0 +1,11 @@
+use super::kinds::ServiceItemKind;
+
+struct ServiceItem {
+    id: i32,
+    database_id: i32,
+    kind: ServiceItemKind,
+}
+
+struct ServiceItemModel {
+    items: Vec<ServiceItem>,
+}