Improve look & feel of HTTP 5xx errors

[kelson42]

Following #710

We would like to display:

Version 3 for 5xx errors in Kiwix Serve.

Text should be:
"Oops. Page isn't working"

"The requested path xyz can not be properly delivered."

[kelson42]

@rgaudin @benoit74 Would you do more? Differently?

[benoit74]

Seems sufficient to me, at least in a first iteration.

[kelson42]

@siemsie May you please make a final proposal?

[rgaudin]

Just to be clear, you are suggesting that we reuse the design of #710 but with different Icon (version 3), Title (Oops. Page isn't working), Leading Text (The requested path can not be properly delivered:) and without the text block. Right?

[siemsie]

Hi all, are we talking something like this?

[benoit74]

LGTM

[kelson42]

@veloman-yunkan Ready to implement I guess.