Use Rust for the front-end too (#374)

Rust can compile to WASM, so let's use it for front-end code as well.

To compile the front-end:

```
cargo install cargo-web
cargo web deploy -p plume-front
```

templates/base.rs.html

@@ -71,6 +71,6 @@
                 <a href="@uri!(instance::admin)">@i18n!(ctx.1, "Administration")</a>
             }
         </footer>
-        <script src="@uri!(static_files: file = "js/menu.js")"></script>
+        <script src="@uri!(static_files: file = "plume-front.js")"></script>
     </body>
 </html>

templates/posts/new.rs.html

@@ -70,5 +70,4 @@
             }
         }
     </form>
-    <script src="@uri!(static_files: file = "js/autoExpand.js")"></script>
 })

templates/search/index.rs.html

@@ -1,6 +1,5 @@
 @use templates::base;
 @use template_utils::*;
-@use routes::*;
 
 @(ctx: BaseContext, now: &str)
 
@@ -26,5 +25,4 @@
     </details>
     <input type="submit" value="Search"/>
   </form>
-  <script src="@uri!(static_files: file = "js/search.js")"></script>
 })