Add link to customize colors

[gikaragia]

As part of better supporting the Site Editor, we updated the 'Customize' links to direct to the Site Editor. However it seems like we still need to rely on the Customizer for users to update the colors in non-block based themes.

It would be a good idea to add a second link, 'Customize Colors' in the Appearance tab in Sensei settings that would redirect the user to the customizer. This link will appear only if the user uses a non-block based themes.