Improve user experience on labels

Description / Overview

Currently, the label system is lacking some features like a list of all existing labels or better feedback during label creation.

Use cases

The users of the system

Feature checklist

• Add a list of all created labels
• Give feedback to the user, that creating/updating a label was successful
• Restyle the UNCHANGED/WILL BE ADDED/WILL BE REMOVED stuff e.g. change UNCHANGED to CURRENT LABELS

(Make sure these are completed before closing the issue, with a link to the relevant commit.)