add ktlint plugin to project and apply default code style (#2209)

* add ktlint plugin to project and apply default code style

* some manual adjustments, fix wildcard imports

* update CONTRIBUTING.md

* fix formatting

app/src/main/java/com/keylesspalace/tusky/util/PickMediaFiles.kt

@@ -49,4 +49,4 @@ class PickMediaFiles : ActivityResultContract<Boolean, List<Uri>>() {
         }
         return emptyList()
     }
-}
+}