QOL: Move source code under the src directory. (#1318)

src/plugins/navigation/back.ts

@@ -0,0 +1,13 @@
+import { BrowserWindow } from 'electron';
+
+import style from './style.css';
+
+import { injectCSS } from '../utils';
+
+export function handle(win: BrowserWindow) {
+  injectCSS(win.webContents, style, () => {
+    win.webContents.send('navigation-css-ready');
+  });
+}
+
+export default handle;