Support dark images for patron logos

• Gather images from ev site and from footer
• Update Canonical logo, add dark images for google, suse, kfocus, gnupg
• There are no dark images for slimbook, tuxedo, and blue-systems, so set background to white
• No more need to have another background color for the kPatrons section in footer

Preview:

Current Light

Proposed Light

Current Dark

Proposed Dark

The same CSS will be applied to patron logos on https://ev.kde.org/supporting-members/ to have it like the following:

	Light	Dark
Current
Proposed