feat: ordered paths

this isn't a very robust solution,
but it is efficent and works on basic filenames.

src/app/mod.rs

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, collections::HashMap, env, path::PathBuf, process};
+use std::{borrow::Cow, collections::BTreeMap, env, path::PathBuf, process};
 
 use iced::{
     Color, Element, Event, Length, Renderer, Subscription, Task, Theme, application, event,
@@ -21,7 +21,7 @@ enum Message {
 
 #[derive(Default)]
 struct State {
-    images: HashMap<PathBuf, Option<widget::image::Handle>>,
+    images: BTreeMap<PathBuf, Option<widget::image::Handle>>,
 
     columns: usize,