Sitemap editor: Add support for color temperature picker

[mherwege]

Closes #2852.

Refs openhab/openhab-core#4420.
Related to openhab/openhab-core#3891.

This PR implements configuring a color temperature picker in the sitemap builder UI.

It also does some visualisation improvements of names and labels (by defaults shows item label in treeview, analogous to model treeview).

[relativeci]

#2504 Bundle Size — 10.87MiB (+0.02%).

1dab231(current) vs b06c21f main#2502(baseline)

Warning

Bundle contains 2 duplicate packages – View duplicate packages

Bundle metrics   4 changes 2 regressions

	Current #2504	Baseline #2502
Initial JS	1.91MiB(+0.34%)	1.91MiB
Initial CSS	577.48KiB(+0.03%)	577.31KiB
Cache Invalidation	22.99%	17.55%
Chunks	226	226
Assets	249	249
Modules	2942(+0.07%)	2940
Duplicate Modules	152	152
Duplicate Code	1.8%	1.8%
Packages	96	96
Duplicate Packages	2	2

Bundle size by type   2 changes 2 regressions

	Current #2504	Baseline #2502
JS	9.08MiB (+0.02%)	9.08MiB
CSS	864.45KiB (+0.05%)	864KiB
Fonts	526.1KiB	526.1KiB
Media	295.6KiB	295.6KiB
IMG	140.74KiB	140.74KiB
HTML	1.38KiB	1.38KiB
Other	871B	871B

Bundle analysis report Branch mherwege:colortemperaturepicker Project dashboard

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[florian-h05]

@mherwege FYI I will try to review this the next days before the next milestone, would be too bad to not have it in 4.3.

[florian-h05]

LGTM, thanks!
Nice refactoring with the mixin.

I found two bugs I fixed myself, you can have a look at my two individual commits.