Setting "importsNotUsedAsValues": "error"

Turning the "importsNotUsedAsValues" TS config value to "error".
This will require us to use `import type` instead of `import` when we are importing a value that is only used as a type (and therefore that is dropped by the Typescript compiler).

Why this change?
This is a requirement to be able to use Svelte in the future. See https://github.com/sveltejs/svelte-preprocess/issues/206#issuecomment-663193798

front/src/Connexion/ConnectionManager.ts

@@ -1,7 +1,7 @@
 import Axios from "axios";
 import {PUSHER_URL, START_ROOM_URL} from "../Enum/EnvironmentVariable";
 import {RoomConnection} from "./RoomConnection";
-import {OnConnectInterface, PositionInterface, ViewportInterface} from "./ConnexionModels";
+import type {OnConnectInterface, PositionInterface, ViewportInterface} from "./ConnexionModels";
 import {GameConnexionTypes, urlManager} from "../Url/UrlManager";
 import {localUserStore} from "./LocalUserStore";
 import {LocalUser} from "./LocalUser";