Right-clicking on new start page

[MatthiasReumann]

Motivation and Context

Currently you can't right-click > open in new tab on the new start page. This PR fixes this.

Description

Use <a :href="" @click.prevent=""> instead of <button>

Steps for Testing

1 Account

1. Log in
2. Right click courses on the side navigation and open in new tab
3. Normal click courses on the side navigation
4. Right click on the course of one livestreams and open in new tab
5. Normal click on the course of one livestream
6. 4. Right click on the course of one VOD and open in new tab
7. Normal click on the course of one VOD

[github-actions]

Your Testserver will be ready at https://1048.test.live.mm.rbg.tum.de in a few minutes.

Logins

Kurs1	Kurs2	Kurs3	Kurs4
public	public	loggedin	enrolled
prof1	prof1	prof2	prof1 prof2
student1 student2 student3	student1 student2	student2 student3	student1 student2

[mono424]

Works like charm 👍