Enhance download of ticket attachments

I also did some code cleanups, e.g. add comments and avoid static calls.

I will also open a new ticket for the rest of the cleanups

I have reviewed this, it's a bit unfortunate that so many off-topic changes are in there. I guess the original purpose of this issue is only in 2 changes of the MR, so I hope I haven't missed anything important.

Thanks for the review. Yes, next time an extra ticket will be opened.

Looking great already. There is only that user load issue left, which could also be handled in a separate issue, if you prefered.

Ah, I now understand what you mean. I will open another ticket for this.

Automatically closed - issue fixed for 2 weeks with no activity.