Extension Preview - Don't show drop down with a single option only

[egamma]

When the workspace is not opened on a folder, then the extension preview should only have a button 'disable' and not a drop down 'disable' with an option 'always'

[sandy081]

Made actions in the viewlet and in the editor to be consistent. They either show one of the two following groups always.

• Enable (Workspace)
• Enable (Always)
  OR
• Disable (Workspace)
• Disable (Always)

If an action is disabled it shows disabled instead of hiding it, which is consistent behaviour across VS Code.