Collapsible grouped notifications

[devBoi76]

This PR adds the long awaited grouped notifications. When there are multiple update notifications of the same project, they are automatically grouped in order to not clutter the notifications page. If more than three are present, a "More" button is shown.

Note: currently notifications are grouped based on their title, as that is the only unique identifier in the notification API. Same thing with the version. In the future it might be a good idea to include those fields in the API.

[devBoi76]

Hold on, I accidentally left in a console.log. I'll remove it real quick

[devBoi76]

Oops, sorry, I missclicked on my phone. Didn't mean to change those :|

[triphora]

Please resolve conflicts!

[devBoi76]

I'll resolve the conflicts some time later this week, probably tomorrow or on Friday

[devBoi76]

Do not merge yet, I'll still make a few changes

[Grawl]

This PR is opened half a year ago. Last commit is three months ago. I still waiting for this feature.

I can help with developing. I know Vue and Nuxt and I'm a frontend developer. Do you need some help?

[Prospector]

We're going to add this feature, but we are going to overhaul how notifications work on the backend first. This feature should come to the site soon!