Fix labelledby to support multiple elements on page

[fcollonval]

The title id for accordion panel and tabbar were not unique if multiple widgets were displayed on the same page. This fixes it.

[blink1073]

Thanks!

[fcollonval]

@meeseeksdev please backport to 1.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 942ab864bcf89dc88246b83c6fb372fa9e05a079

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #407: Fix labelledby to support multiple elements on page'

4. Push to a named branch:

git push YOURFORK 1.x:auto-backport-of-pr-407-on-1.x

5. Create a PR against branch 1.x, I would have named this PR:

"Backport PR #407 on branch 1.x (Fix labelledby to support multiple elements on page)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.