Fix paths

Replaced backslashes in paths with slashes. I did
not touch function that do the same with paths.
Those can be removed manually.
Also dataDir() returns a path that ends with a
slash so I got rid of duplicated slashes.

src/utils/themes.ts

@@ -40,7 +40,7 @@ const defaultTheme = {
 export async function getThemeList() {
   // Do some invoke to backend to get the theme list
   const themes = (await invoke('get_theme_list', {
-    dataDir: `${await dataDir()}/cultivation`,
+    dataDir: `${await dataDir()}cultivation`,
   })) as BackendThemeList[]
   const list: ThemeList[] = [
     // ALWAYS include default theme