Show Plugwise configuration-link on gateway only

[bouwew]

Proposed change

Show the Plugwise configuration_url only on the gateway device.
Adding some minor code optimizations.

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• Dependency upgrade
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[home-assistant]

Hey there @CoMPaTech, mind taking a look at this pull request as it has been labeled with an integration (plugwise) you are listed as a code owner for? Thanks!

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[joostlek]

This last commit will only work if we actually update the data object instead of receiving new objects. Previously we always fetched it from the coordinator, and if it wasn't there, it was unavailable. Now it's always there, but who knows if its up to date

[bouwew]

Thanks for reviewing! @joostlek