More tests, not found page and dashboard fixes

When post was deleted, website shows a 404 page insead of an 500 page.
Also made the dashboard empty page message more explicit.

src/routes.rs

@@ -25,7 +25,7 @@ pub use unsubscribe::*;
 
 use crate::{
     authentication::AuthError,
-    templates::{InternalErrorTemplate, MessageTemplate, NotFoundTemplate},
+    templates::{HtmlTemplate, InternalErrorTemplate, MessageTemplate, NotFoundTemplate},
 };
 
 pub fn generate_token() -> String {
@@ -155,9 +155,6 @@ impl From<AuthError> for AppError {
 }
 
 pub async fn not_found() -> Response {
-    (
-        StatusCode::NOT_FOUND,
-        Html(NotFoundTemplate.render().unwrap()),
-    )
-        .into_response()
+    let template = HtmlTemplate(NotFoundTemplate);
+    (StatusCode::NOT_FOUND, template).into_response()
 }