add loading message to mail and contacts list

[johndoh]

for #9006

adds support for 2 additional labels into the Elastic skin data-label-msg-loading and data-label-msg-empty on list objects and uses those in the mail and addressbook templates to display a loading message in the list while the request is running.

this does not break any, BC. data-label-msg is still supported for simpler lists

makes the "this list is empty" message only show after loading/searching is complete, when changing mailboxes or until the loading/searching action is complete nothing is shown.

[pabzm]

Looks good and works, thank you very much!

[pabzm]

(@alecpl Just for clarity: I'm reviewing things but am currently not merging until you've had a chance to add your thoughts or we a grooved into a new workflow.)

[pabzm]

@alecpl Please have a look at this and provide feedback, or let us know that you're fine with us proceeding without your involvement.

[github-actions]

@pabzm, @alecpl
🛎️ This PR has had no activity in two weeks.

[pabzm]

@alecpl Please respond in the open thread of this PR. (I'll take over and decide on my own after one more week of silence.)

[pabzm]

/remind me to merge this in one week

[github-actions]

@pabzm set a reminder for 12/9/2024

[johndoh]

i have simplified the change. i think the important thing is the "list is empty" message does not display while the loading or searching actions are running

[github-actions]

👋 @pabzm, merge this

[pabzm]

@johndoh Thank you for reducing your change to a state that's agreeable to all!

Could you fix the message of the first commit, please? (Contains a backslash instead of a quotation mark)

[johndoh]

@pabzm fixed, sorry I didn't notice that before and thanks for the changelog text

[pabzm]

@johndoh I allowed myself to resolve the conflict, since it was trivial and was caused by the Changelog line I wrote.

Thanks again for this contribution!

[alecpl]

I'd prefer PRs to be squashed on merge.