Avoid duplicate labels from Key-Values

[will-moore]

Fixes #395

To test:

• Add duplicate Key-Value pairs to an Image
• Choose that Key when adding labels to the image from key-value pairs.
• Only 1 label should be created on each Panel for the duplicate Key-Value pairs.

[jburel]

Discussed with @will-moore, it is currently not possible to add kvp in web using merge-ci.
This is currently broken

[will-moore]

@jburel Thanks for finding that. Fixed in open PR: ome/omero-web@60dece6

[jburel]

using https://merge-ci.openmicroscopy.org/web/webclient/?show=image-83165 (user-1)

• created a duplicate kvp
• in figure, only one key listed

* I can add the same kvp multiple times (unexpected)

* only one entry in the right-hand panel for the kvp (see screenshot) * Click on red cross to remove, remove all the duplicated entries

[will-moore]

Ah, that's a slightly different issue. In that case you have chosen to add the same label repeatedly, which will cause the same issue, regardless of whether it comes from KV pairs, or other metadata or is added manually.
I'm not sure that this is really a bug. Although you could consider the batch edit and delete behaviour to be unexpected. But that behaviour has always been the same an no-one has complained so I think it would need more discussion to change it and is outside the scope of #395 so I would prefer to just get the existing fix in for now.