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/Phaser/Entity/SpeechBubble.ts

@@ -1,12 +1,12 @@
 import Scene = Phaser.Scene;
-import {Character} from "./Character";
+import type {Character} from "./Character";
 
 //todo: improve this WIP
 export class SpeechBubble {
     private bubble: Phaser.GameObjects.Graphics;
     private content: Phaser.GameObjects.Text;
 
-    
+
     constructor(scene: Scene, player: Character, text: string = "") {
 
         const bubbleHeight = 50;