Added grouped and custom option support to `<GhTokenInput>`
Added grouped and custom option support to `<GhTokenInput>`

no issue

- `<GhTokenInput>` is based around `<PowerSelect>` but using Power Select's grouped options feature didn't work because we weren't falling back to it's built-in group component
- updated the `<GhTokenInput>` template to use a supplied block as the option display rather than only displaying the option's label (allows for counts etc to be shown alongside dropdown options)

TryGhost/Ghost-Admin,TryGhost/Ghost-Admin