Clean up field type prevalues UI

[ronaldbarendse]

The prevalues within a field type configuration contains some UI glitches:

• Hovering the trash-can shows an underline
• Removing shows a plain/browser confirmation dialog
• The add button isn't aligned with the text input
• The prevalue source select is shown after the title, instead of below
• The prevalue source initially contains an empty option (and could probably just be hidden if no sources are available)

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This item has been added to our backlog AB#5505

[ronaldbarendse]

The confirmation could be updated as part of #197.

[nikolajlauridsen]

These has been fixed, and should be in the next release 👍