Add typescript support for helper functions (#598)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/598
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

src/types/shims-tsx.d.ts

@@ -0,0 +1,13 @@
+import Vue, { VNode } from 'vue'
+
+declare global {
+  namespace JSX {
+    // tslint:disable no-empty-interface
+    interface Element extends VNode {}
+    // tslint:disable no-empty-interface
+    interface ElementClass extends Vue {}
+    interface IntrinsicElements {
+      [elem: string]: any
+    }
+  }
+}

src/types/shims-vue.d.ts

@@ -0,0 +1,4 @@
+declare module '*.vue' {
+  import Vue from 'vue'
+  export default Vue
+}