Display error in a nicer way when post couldn't be found

[Fxsch]

Pre-Flight checklist

• [X] Did you check to see if this issue already exists?
• [X] This is a single feature request. (Do not put multiple feature requests in one issue)
• [X] This is not a question or discussion. (Use https://lemmy.ml/c/jerboa for that)

Describe The Feature Request Below

When clicking a post that the app/server can't find anymore, you get this screen:

I think it would be a good idea to display this in a nicer looking way with a text that say something like This post couldn't be found and buttons to go back or refresh.