refs. https://github.com/TryGhost/Ghost/issues/11342
- replaced Zapier and Amp logos for SVGs with transparent background so that there's no white background in night shift
- inverted Unsplash icon in night shift (similarly to Mailchimp, Typeform etc.)
- replaced ellipsis icon for SVG and handled night shift color change
- removed unnecessary icon container drop shadow in integration detail pages for night shift
