Print GUI - Cache database queries for reuse.

This allows users to hit a slow-down when cycling between weeks, but
going back to the same week will hit the cache.

For workloads with large numbers of database entries, this is expected
to improve user expererience performance a lot - at the cost of extra
memory usage.

core/src/storage.rs

@@ -312,7 +312,7 @@ fn insert_new_entry_rows_into_database(
 //
 // Allows filtering the full list of entries by a sub-set of
 // times/dates (without having to fetch data from the database).
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct Entries {
     start_datetime: chrono::DateTime<chrono::Local>,
     end_datetime: chrono::DateTime<chrono::Local>,

print-gui-bin/src/main.rs

@@ -1,4 +1,6 @@
 use crate::main_window::build_ui;
+use crate::main_window::GlobalEntries;
+use crate::main_window::GlobalEntriesRcRefCell;
 use crate::main_window::GlobalState;
 use crate::main_window::GlobalStateRcRefCell;
 use crate::settings::CommandArguments;
@@ -41,11 +43,12 @@ fn main() -> Result<()> {
 
     let global_state: GlobalStateRcRefCell =
         Rc::new(RefCell::new(GlobalState::new_with_settings(settings)));
+    let global_entries: GlobalEntriesRcRefCell = Rc::new(RefCell::new(GlobalEntries::new()));
 
     application.connect_activate(clone!(
         @strong global_state =>
             move |app| {
-                build_ui(app, global_state.clone())
+                build_ui(app, global_state.clone(), global_entries.clone())
             }
     ));