Update appearance of editor

[janfaracik]

WIP.

Before

After

Key changes

• Use Jenkins color palette
• Increase height from 250px to 350px
• Use system monospace font
• Icons and animations updated
• Removed Pipeline Syntax link in favour of parent plugin's description

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[daniel-beck]

I expect that nobody will find the new link location in the description. Could it be made more visible?