Adding a global error message

This error message should be used for non fatal errors (otherwise, use the ErrorScene).
It is implemented using Svelte and the new "$errorStore".

Use `errorStore.addErrorMessage` to display the error popup with the message.

This PR uses this error message to display a popup explaining the browser is too old for WebRTC.

front/src/Components/UI/ErrorDialog.svelte

@@ -0,0 +1,44 @@
+<script lang="ts">
+import {errorStore} from "../../Stores/ErrorStore";
+
+function close(): boolean {
+    errorStore.clearMessages();
+    return false;
+}
+
+</script>
+
+<dialog class="error-dialog nes-dialog is-dark is-rounded" id="dialog-dark-rounded" open>
+    <p class="nes-text is-error title">Error</p>
+    <div class="body">
+    {#each $errorStore as error}
+    <p>{error}</p>
+    {/each}
+    </div>
+    <div class="button-bar">
+        <button class="nes-btn is-error" on:click={close}>Close</button>
+    </div>
+</dialog>
+
+<style lang="scss">
+    dialog.error-dialog {
+      pointer-events: auto;
+      top: 10%;
+
+      .button-bar {
+        text-align: center;
+      }
+
+      .body {
+        max-height: 50vh;
+      }
+
+      p {
+        font-family: "Press Start 2P";
+
+        &.title {
+          text-align: center;
+        }
+      }
+    }
+</style>